[PATCH] arch/ppc/kernel/idle.c: don't declare cpu variable in non-SMP kernels

Disable declaration of cpu variable in default_idle function when
building non-SMP kernels.

Signed-off-by: Otavio Salvador <otavio@debian.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>