cpufreq: brcmstb-avs-cpufreq: AVS CPUfreq driver for Broadcom STB SoCs

This driver supports voltage and frequency scaling on Broadcom STB SoCs
using AVS firmware with DFS and DVFS support.

Actual frequency or voltage scaling is done exclusively by the AVS
firmware. The driver merely provides a standard CPUfreq interface to
other kernel components and userland, and instructs the AVS firmware to
perform frequency or voltage changes on its behalf.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>