libxc: allocate memory with vNUMA information for PV guest

libxc: allocate memory with vNUMA information for PV guest

From libxc's point of view, it only needs to know vnode to pnode mapping
and size of each vnode to allocate memory accordingly. Add these fields
to xc_dom structure.

The caller might not pass in vNUMA information. In that case, a dummy
layout is generated for the convenience of libxc's allocation code. The
upper layer (libxl etc) still sees the domain has no vNUMA
configuration.

Note that for this patch on PV x86 guest can have multiple regions of
ram allocated.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Elena Ufimtseva <ufimtseva@gmail.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>