x86/vm_event: add hvm/vm_event.{h,c}

x86/vm_event: add hvm/vm_event.{h,c}

Created arch/x86/hvm/vm_event.c and include/asm-x86/hvm/vm_event.h,
where HVM-specific vm_event-related code will live. This cleans up
hvm_do_resume() and ensures that the vm_event maintainers are
responsible for changes to that code.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>