drivers/cpufreq: Add a CPUFreq driver for AMD processors (Fam17h and later)

Add a new CPUFreq driver which exposes sysfs entries to control the
platform. To make use of this driver use a kernel commandline option.

Ex: amd_cpufreq=enable	- Enable AMD CPUFreq driver for Fam17h and later

Also, place amd-cpufreq before acpi-cpufreq in the Makefile to give it
higher priority.

Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>