GRU Driver: page faults & exceptions

This file contains the functions that manage GRU page faults and
exceptions.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>