[CPUFREQ] Kconfig powernow-k8 driver should depend on ACPI P-States driver

powernow-k8 really needs to use ACPI to function on SMP systems.
The current Kconfig allows us to build kernels which fail mysteriously
for some users due to us trying to automatically enable this, and
getting it wrong.  It's easier to just present this as an option
to the user.

Signed-off-by: Joshua Hoblitt <jhoblitt@ifa.hawaii.edu>
Signed-off-by: Dave Jones <davej@redhat.com>