s390: use generic percpu linux-2.6.git

Change s390 percpu.h to use asm-generic/percpu.h

Signed-off-by: Mike Travis <travis@sgi.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>