vm_event: sanitize vm_event response handling

vm_event: sanitize vm_event response handling

Setting response flags in vm_event are only ever safe if the vCPUs are paused.
To reflect this we move all checks within the if block that already checks
whether this is the case. Checks that are only supported on one architecture
we relocate the bitmask operations to the arch-specific handlers to avoid
the overhead on architectures that don't support it.

Furthermore, we clean-up the emulation checks so it more clearly represents the
decision-logic when emulation should take place. As part of this we also
set the stage to allow emulation in response to other types of events, not just
mem_access violations.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>