sgi-xp: use standard bitops macros and functions

Change sgi-xp to use the standard bitops macros and functions instead of
trying to invent its own mechanism.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>