sgi-xp: define is_shub() and is_uv() macros

Define the is_shub()/is_uv() macros if they've not already been defined.

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>