gru: support 64-bit GRU addresses

Increase the maximum address supported by the SGI GRU driver to a full 64
bits.  Note that GRU addresses are not always the same as socket virtual
addresses.  Sockets may not necessarily support the full 64 bits.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>