x86/vm_event: add HVM debug exception vm_events

x86/vm_event: add HVM debug exception vm_events

Since in-guest debug exceptions are now unconditionally trapped to Xen, adding
a hook for vm_event subscribers to tap into this new always-on guest event. We
rename along the way hvm_event_breakpoint_type to hvm_event_type to better
match the various events that can be passed with it. We also introduce the
necessary monitor_op domctl's to enable subscribing to the events.

This patch also provides monitor subscribers to int3 events proper access
to the instruction length necessary for accurate event-reinjection. Without
this subscribers manually have to evaluate if the int3 instruction has any
prefix attached which would change the instruction length.

Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>