xen: Introduce monitor_op domctl

xen: Introduce monitor_op domctl

In preparation for allowing for introspecting ARM and PV domains the old
control interface via the hvm_op hypercall is retired. A new control mechanism
is introduced via the domctl hypercall: monitor_op.

This patch aims to establish a base API on which future applications can build
on.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Tim Deegan <tim@xen.org>