x86/uv: fix init of memory-less nodes

Add support for nodes that have cpus but no memory.
The current code was failing to add these nodes
to the nodes_present_map.

v2: Fixes case caught by David Rientjes - missed support
    for the x2apic SRAT table.

[ Impact: fix potential boot crash on memory-less UV nodes. ]

Reported-by: David Rientjes <rientjes@google.com>
Signed-off-by: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20090417142242.GA23743@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>