CA-138930:Xapi should not call domain_set_memmap_limit for HVM
domains.

Since Xen 4.2 the hypercall behind xc_domain_set_memmap_limit() is not
permitted for HVM domains. Xapi should only call this for PV domains.

Signed-off-by: Akshay <akshay.ramani@citrix.com>
Merge pull request #1812 from akshayramani/CA-138930

CA-138930: Xapi should not call domain_set_memmap_limit for HVM