Xen vNUMA for PV guests.

Defines XENMEM subop hypercall for PV vNUMA
enabled guests and provides vNUMA topology
information from per-domain vnuma topology build info.

Changes since v1:
- changed type from int to uint and unsigned in vNUMA structures;
- removed unecessary file vnuma.h as requested in review
- added domain_vnuma_destroy;
- fixed usage of rcu_lock_domain_by_any_id;
- removed unecessary guest_handle_cast calls;
- coding style fixes;

Signed-off-by: Elena Ufimtseva <ufimtseva@gmail.com>