Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

Revert "Cache FPU enable state on all platforms"

This reverts commit 186180cf309b365b45c162f7a1f5931f0fc05d7c.

Cache FPU enable state on all platforms

This change broadens the caching of the FPU enable/disable bit from arm
to all platforms to ensure that on x86 time is not wasted on the
fastpath disabling or enabling an already disabled/enabled FPU.

Revert the recent changes to Faster FPU switch

These changes need to be reverted until we can properly test the changes
with all of our hardware online (currently we cannot test on x86
hardware).

This reverts commit a0aeec3b304d16909619bc847197df221c73a0c4.
This reverts commit af0fdc82c23f1e7e3f1e568f6987f5afd0d2150a.
This reverts commit a190a14ecaae688a6b40dd0a699b8f49c2c0631e.

Cache FPU enable state on all platforms

This change broadens the caching of the FPU enable/disable bit from arm
to all platforms to ensure that on x86 time is not wasted on the
fastpath disabling or enabling an already disabled/enabled FPU.

style: consistently attach return type

Add attach-return-type to astyle

Move arch independent functions to generic files and HAVE_FPU config

x86: move current active FPU owner to node state

x86: define number of restore since switch as node state

x86: Permit larger than required XSAVE regions

Instead of failing when the configured XSAVE region size is larger than required
this changes to print out a warning instead.

x86: Initialize store area when using XSAVE variant instructions

When using, SSE (and other variants), mxcsr would assume similar role as
control word in i387 FPU. When initializing the FPU, it should have valid value.

x86: Rewrite config_default as config_ternary for FPU

config_default was intended to either evaluated to the passed configuration
value, or the a default value if the config didn't exist. For integer values
this does not actually work, and the default value always gets returned.
This commit reimplements the desired functionality as config_ternary, which
takes 3 arguments, a config to switch on and a desired true and false expansion

x86: Switch to NULL FPU state if suspect no one using it

Adds a heuristic to switch to a NULL fpu state if we think the FPU
is not presently in use. A NULL fpu state is more efficient as
we do not have to enable/disable the FPU when switching threads

Remove unneeded usages of `VISIBLE`

Using `VISIBLE` where it is not needed limits the ability for the
compiler to optimize, especially when using whole program optimizations

Store remote FPU state

x86: Always consider FPU owernship of threads core

When checking if a thread is using the FPU or not we now check on that
threads core, under the assumption that if a thread migrates its FPU
state is explicitly (and not lazily) migrated.

SELFOUR-287: 32-bit vt-x implementation

This is an implementation of vt-x for x86 kernels running in
ia32 mode.

SELFOUR-632: implement cores non-architecture dependent structres

SELFOUR-630:preliminary booting application processors
- update core detection code and Kconfig file
- update kernel stack managment so that BSP does not use boot stack before IPI APs
- move arch dependant data to a single structure
- add cache line size to Kconfig
- add cpu indexing and apic id mapping
- boot APs to halting state
- add guard for kernel stack if there is only one core

Revert "Merge pull request #358 in SEL4/sel4 from ~AZARRABI/sel4:multicore to master"

This reverts commit ce2f666bb811c5e4c779829fcb09d5a189ebcdbb, reversing
changes made to dc183f96b81f2344d7d0d910fc430f924eaae940.

SELFOUR-630:preliminary booting application processors
- update core detection code and Kconfig file
- update kernel stack managment so that BSP does not use boot stack before IPI APs
- move arch dependant data to a single structure
- add cache line size to Kconfig
- add cpu indexing and apic id mapping
- boot APs to halting state
- add guard for kernel stack if there is only one core

SELFOUR-615: arm entry point stubs

Provide generic C entry/exit hook routines

It can be deseriable to run code before/after user mode, but
not have to write it in assembly. This commit adds such stubs
that get called as the first/last C code when coming in
and out of the kernel

trivial: style

x86: Introduce support for XSAVE feature set

The XSAVE feature set is the future proof way for x86 CPUs to
manage extended CPU state. Extended state is MMX, FPU, SSE, AVX etc
registers. This is a replacement for the current FXSAVE and the
512 byte FPU region.

XSAVE introduces a few problems that this commit has to address

* The alignment of the XSAVE region is 64bytes, instead of the 16
bytes of the FXSAVE region
* XSAVE region size is dependent on the desired features, which
are detected at run time
* There are multiple variants of the XSAVE instruction that have
different potential optimizations, but are not always supported

The solutions to these are

* Re-order the FPU state and user registers in the user context
struct so that the new XSAVE region is first, and is thus
aligned to 64bytes without needing lots of padding
* Provide config options for desired features (including XSAVE
instruction variant) and required XSAVE region size. These
are checked at boot time to ensure the CPU meets these
requirements

x86: Rename ia32->x86

This is a stylistic commit to make names of variables/constants and
functions in the kernel more consistent. That is, things that are
not IA32 specific, but are generic x86, get renamed to having an
x86 name

refactor tcb_t to remove duplication between x86 and arm header files

x86: Make x86 the name of the architecture instead of IA32

IA32 is 32bit version of the x86 architecture. Whilst only IA32
is supported, much of the code is generic x86. Using a generic
x86 architecture will aid in future 64bit support