x86: rework hypercall argument translation area setup

x86: rework hypercall argument translation area setup

... using the new per-domain mapping management functions, adding
destroy_perdomain_mapping() to the previously introduced pair.

Rather than using an order-1 Xen heap allocation, use (currently 2)
individual domain heap pages to populate space in the per-domain
mapping area.

Also fix a benign off-by-one mistake in is_compat_arg_xlat_range().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>