move XENMEM_add_to_physmap_range handling framework to common code

move XENMEM_add_to_physmap_range handling framework to common code

There's really nothing really architecture specific here; the
architecture specific handling is limited to
xenmem_add_to_physmap_one().

This further eliminates the erroneous bailing from
xenmem_add_to_physmap_range() if xenmem_add_to_physmap_one() fails.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>