riscv: Implement benchmark log buffer

Can now perform benchmarks on the kernel using the log buffer to trace
kernel behavior.

Signed-off-by: Curtis Millar <curtis.millar@data61.csiro.au>

libsel4: fix license tags

These files should have been released under BSD-2-Clause in the first
place (as per parent LICENSE.md file).

Closes #245

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

Do not generate data symbols for enums

With clang 11 these become bss symbols rather than commons, resulting in
multiple definition errors at link time. gcc 10 is likely to expose the
same issue.

Signed-off-by: Stefan O'Rear <sorear@fastmail.com>

libsel4,riscv: Remove seL4_UserException_FLAGS

This field is unused and is never set to anything by the kernel. Other
architecture definitions of seL4_UserException_Msg contain an equivalent
field for a current-program-status-register-like register that the fault
handler can read and modify as part of fault handling. RISC-V's
equivalent register SSTATUS doesn't contain any fields that would be
useful for a fault handler to modify at this stage and so the register
isn't transferred in the fault.

Signed-off-by: Kent McLeod <Kent.Mcleod@data61.csiro.au>

replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

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.

riscv32 does not support huge pages

For some reason the kernel documented and maintained constants for a
512MiB 'huge page' in riscv32 which is not part of the specification.

The references and constants are removed

mcs: Update size constants for RISC-V

Update the notification size constant for the larger notification of MCS
and add the constant for the size of the reply object.

mcs: Timeout fault and reply for RISC-V

Add fault and reply for timeout faults on RISC-V.

trivial: VspaceBits -> VSpaceBits on riscv32

libsel4: add seL4_VspaceBits

This constant represents the size of the root page table.

libsel4,riscv: Hide enums for non-C preprocessing

sel4/sel4_arch/constants.h gets used to provide constants in linker
files and we want to avoid generation of enum definitions

More standard constant name, moved ASID constants to arch generic files

riscv/spike: fix seL4_UserTop for riscv

Use correct values and document them.

Add seL4_UserTop and move kernelBase to the arch level

- seL4_UserTop is a new constant which represents the top of virtual
memory available to user level
- this commit also rationalises several constants (USER_TOP, kernelBase)
and moves them to the arch level, such that ports only need to define
seL4_UserTop.

riscv: use one definition of page bits

riscv: build on 32 bit

SELFOUR-1276: set PrefetchFault MR for riscv

This was being tracked in the fault_t, but not set as part of the
message to the user.

[SELFOUR-1156] RISC-V Port

Experimental release that supports both RV32 and RV64