x86: UV, SGI RTC: loop through installed UV blades

Add macro to loop through each possible blade.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: john stultz <johnstul@us.ibm.com>
LKML-Reference: <20090304185719.GB24419@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>