pvh: use PV handlers for PIO

pvh: use PV handlers for PIO

Register an IO handler for the entire PIO range, and have it call the
PV PIO handlers.

NB at this point this won't do the full "copy and execute on the stack
with full GPRs" work-around; this may need to be sorted out for dom0 to allow
these instructions to happen in guest context.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Eddie Dong <eddie.dong@intel.com>