schema: Allow > UINT_MAX KiB of memory for NUMA nodes

schema: Allow > UINT_MAX KiB of memory for NUMA nodes

Using more than 4TiB of memory per NUMA node would not be possible to
express in the XML without violating the schema. Not that such boxes
would be common, but we should use a longer type at this point.

The pattern is not necessary since libvirt redefines the type already in
basictypes.rng with the same pattern.