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

libsel4vm: Advance fault in apic fault callback

Fixed an issue with the x86 'apic_fault_callback' where it
doesn't advance the vcpu fault before returing 'FAULT_HANDLED'.
Returning the 'FAULT_HANDLED' code assumes the vcpu state has been
appropriately updated before resuming. Without this update the VM
would keep faulting on the same apic access instruction.

trivial: Style changed files

libsel4vm*: Switch malloc calls to calloc

Reduces chances of an uninitialised structure being used and causing
issues that are painful to debug.

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: Made x86 interrupt interface private

The usage of the interrupt functions is only performed
internally. Moved the interrupt header and source into x86
architecture directory such that that implementation is private.

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.