x86/monitor: Notify monitor if an emulation fails.

x86/monitor: Notify monitor if an emulation fails.

If case of a vm_event with the emulate_flags set, if the instruction
is not implemented by the emulator, the monitor should be notified instead
of directly injecting a hw exception.
This behavior can be used to re-execute an instruction not supported by
the emulator using the real processor (e.g. altp2m) instead of just
crashing.

Signed-off-by: Petre Pircalabu <ppircalabu@bitdefender.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>