gru: support instruction completion interrupts

Add support for interrupts generated by GRU instruction completion.
Previously, the only interrupts were for TLB misses.  The hardware also
supports interrupts on instruction completion.  This will be supported for
instructions issued by the kernel.

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>