xen: enable XENMEM_memory_map in hvm

xen: enable XENMEM_memory_map in hvm

This patch enables XENMEM_memory_map in hvm. So hvmloader can
use it to setup the e820 mappings.

CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <jbeulich@suse.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>