tools/libxenforeignmemory: add support for resource mapping

tools/libxenforeignmemory: add support for resource mapping

A previous patch introduced a new HYPERVISOR_memory_op to acquire guest
resources for direct priv-mapping.

This patch adds new functionality into libxenforeignmemory to make use
of a new privcmd ioctl [1] that uses the new memory op to make such
resources available via mmap(2).

[1] http://xenbits.xen.org/gitweb/?p=people/pauldu/linux.git;a=commit;h=ce59a05e6712

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>