libvirt: enhance to return avail free pages on cells

Update driver libvirt to return avail free pages memory
on numa cells.

Work-Item: Enhance libvirt driver to report available
           large pages per NUMA node in the host state data

Change-Id: If2e5b509df2a32464d040cd79b29368b60513cff
Partial-Implement: blueprint virt-driver-large-pages
Merge "libvirt: enhance to return avail free pages on cells"