x86/monitor: add support for descriptor access events

x86/monitor: add support for descriptor access events

Adds monitor support for descriptor access events (reads & writes of
IDTR/GDTR/LDTR/TR) for the x86 architecture (VMX and SVM).

Signed-off-by: Adrian Pop <apop@bitdefender.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
[jb: minor cosmetic (hopefully!) cleanup]
Reviewed-by: Jan Beulich <jbeulich@suse.com>