X86_POWERNOW_K8_ACPI must depend on ACPI

X86_POWERNOW_K8_ACPI must depend on ACPI

This patch fixes the following compile error introduced by
commit e8666b2718fdb5bf0ea7c3126f7e292bbbf2946b and reported
by Alexey Dobriyan:

<--  snip  -->

   CC      arch/i386/kernel/acpi/cstate.o
In file included from arch/i386/kernel/acpi/cstate.c:17:
include/acpi/processor.h:88: error: expected specifier-qualifier-list before 'acpi_integer'

<--  snip  -->

If you select something you must ensure that the dependencies of what
you are selecting are fulfilled.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Joshua Hoblitt <jhoblitt@ifa.hawaii.edu>
Cc: Dave Jones <davej@redhat.com>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>