libvirt: introduce config to handle cells memory pages caps

Introduces a new config 'LibvirtConfigCapsNUMAPages' to
the driver libvirt which handles memory pages capabilities
of the host in the context of NUMA.

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

Partial-Implement: blueprint virt-driver-large-pages
Change-Id: I902510c190a1b85d860f2579b01b52bb13f4d034
Merge "libvirt: introduce config to handle cells memory pages caps"