Convert to SPDX license tags

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

libsel4vm: Duplicate x86 decode instructions

Removed duplicated x86 decode instruction definitions in the
single op decode table.

libsel4vm: Remove init in x86 instr decoding

As the instruction definitions in the x86 instruction decoding
table are constant and in a static location we can define them
directly in the decoding tables. This removes the need to call
an initialisation function.

libsel4vm: Style x86 decode source

Trivial styling on processor/decode.c

libsel4vm: Updated license header in x86 decode.c

Updated license header year.

libsel4vm: Support for multi-byte x86 opcodes

This adds support for decoding the multi-byte x86 instruction MOVQ
(Move Quadword). This being a faulting instruction the Linux
guest performs on MMIO regions we emulate. Introducing support for
MOVQ results in adding a new instruction decoding table for double
op instructions.

libsel4vm: Refactoring of x86 instruction decoding

This commit refactors the x86 instruction decoding in-order to
make its implementation is more modular and easier to read and
update. The key changes being::
* moving "magic" instruction value constants into enum
definitions
* initialisation of an instruction decoding table that associates
a single op instruction with a decoding handler - simplifying
the 'vm_decode_instruction' function

trivial: Style changed files

libsel4vm: Removed uses of 'vmm' in x86 source

Updated x86 source such that the naming convention used is to
prefix/postfix with 'vm' rather than 'vmm'. This change makes
the naming convention consistent as this library now represents a
single 'vm' instance rather than a vmm.

libsel4vm: arch specific includes into arch subdir

Moved the architecture specific headers, being unique header files
that only exist for a given architecture, into an 'arch'
subdirectory. Since this library can be used across architectures
this avoids polluting the root libsel4vm namespace and adds
further structure to distinguish different interfaces.

libsel4vm: x86 processor src as private interface

Moved the x86 processor source and header into the x86
architecture subdirectory. This has been transformed into an
private interface that only internal code can access. We choose
to abstract over processor source. Updated the processor header
includes to reflect this change.