APM support depends on CONFIG_PM_SLEEP

Commit 296699de

 broke building APM
support if CONFIG_PM_SLEEP is not set.

Reported by Toralf Förster <toralf.foerster@gmx.de>

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
[ Simplified a bit as suggested by Rafael.   -Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>