devfreq: Add MSM CPUfreq governor

The MSM CPUfreq devfreq governor determines the CPU to DDR bandwidth vote
based on the current CPU frequency of all the active CPUs.

This functionality used to be a part of the MSM CPUfreq driver that
directly voted for the CPU to DDR bandwidth using MSM bus scaling APIs.
This refactor decouples CPU to DDR BW scaling from CPU frequency and allows
switch between various CPU BW governors.

The bandwidth values in the msm-cpufreq table have to be updated since the
new CPU BW driver does the MBps to Bps conversion correctly. The MSM
CPUfreq driver used to do * 1000 * 1000 to convert from MBps to Bps instead
of doing * 1024 * 1024.

Change-Id: I184f09d628a1b27d52506d2f760d65831f1a1110
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
(cherry picked from commit 4bbc993b178bca1969f2e4b122a32e0e589ee839)

Conflicts:
	arch/arm/boot/dts/msm8974.dtsi
	arch/arm/mach-msm/Kconfig
	arch/arm/mach-msm/devfreq_cpubw.c
	drivers/devfreq/Kconfig
	drivers/devfreq/Makefile