Convert to SPDX license tags

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

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: Moved remaining x86 platform includes

Moved the remaining x86 platform includes [vmcs.h and vmexit.h]
into the x86 arch include directory. This are still relevant to
to this library and not necessarily platform specific (such that
it should exist libsel4vmmplatsupport).

libsel4vm: Made vmm sync guest functions private

Moved the vmm sync guest functions in the x86 source into private
interfaces. Additionally updated the locations of the
implementation to the guest_state and context sources in order
to keep the sources consolidated.

libsel4vm: Add x86 guest state initialisation

Added a helper function to the guest state interface for setting
the datastructure to a default state.

libsel4vm: Refactored x86 vmcs interface

The vmcs interface has been made private, this ensuring the guest
x86 context interface is the only interface with public methods for
updating vmcs fields. This ensures external vmcs updates are always
consistent with our internal shadow state. The vmcs read and write
helpers have been merged into the guest x86 context implementation
and made privately available to our internal source.

libsel4vm: Removed vmm_[read|set]_user_context

This is now implemented by the guest x86 context interface.
Updates source to use 'vm_[get|set]_thread_context_reg'.

libsel4vm: Make guest_state interface private

Make the guest_state interface a private header as we don't want
to expose this to the user. Updated the internal source to include
the private header.