msm: cpufreq: Move cpufreq to drivers/cpufreq/

Architecutural changes in the ARM Linux kernel tree mandate the
eventual removal of the mach-* directories. Move mach/cpufreq to
driver/cpufreq/. Also move related header to include/linux.

Change-Id: I6dcf69e275b7ca7ba913e945353a42f0d6321731
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>