cpufreq: Remove support for hardware P-state chips from powernow-k8

These chips are now supported by acpi-cpufreq, so we can delete all the
code handling them.

Andre: Tighten the deprecation warning message. Trigger load of
acpi-cpufreq and let the load of the module finally fail.
This avoids the problem of users ending up without any cpufreq support
after the transition.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>