gru: bug fixes for GRU exception handling

Bug fixes for GRU exception handling.  Additional fields from the CBR must
be returned to the user to allow the user to correctly diagnose GRU
exceptions.

Handle endcase in TFH TLB miss handling.  Verify that TFH actually
indicates a pending exception.

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>