Convert to SPDX license tags

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

libsel4vm: Made 'vm_memory_handle_fault' private

Made the interface function 'vm_memory_handle_fault' a private
function as this is only used internally within libsel4vm.

libsel4vm: Return if ept fault is handled

Prior the 'ept_violation_handler' advanced the instruction pointer
after receiving a 'FAULT_HANDLED' from the registered vm memory
fault handler. It is general practice that the registered
callback updates fault state (e.g current eip) and 'FAULT_HANDLED'
simply resumes the VM. This change potentially avoids advancing
the instruction pointer twice, leading to an invalid machine
state.

libsel4vm: Remove register check in ept handler

The register value returned from 'vm_decode_ept_violation' can be
less then 0 if the decode instruction is a MOV with immediate
value. This check results in the VM crashing when decoding a
MOV with immediate instruction which could otherwise be handled.

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.

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: Moved x86 src in arch sub-directory

Moved the last relevant x86 source in 'sel4-x86-vmm' into the
appropriate x86 source subdirectory. This commit just tidies up
the x86 source post refactors.