x86, uv: Add function retrieving node controller revision number

Add function for determining the revision id of the SGI UV
node controller chip (HUB). This function is needed in a
subsequent patch.

Signed-off-by: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20100112210904.GA24546@sgi.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>