arm64: Select PM_OPP on MSM architectures

The Operating Power Point library provides a framework
for the storage and communication of frequency-to-voltage
tables between drivers and modules. Select it on MSM
architectures. Normally this would be selected by the
architecture's CPUFREQ Kconfig, but since the latter is
selected by ARCH_MSM, place the OPP config there as well.

Change-Id: I9cec1bf84632a08a5d45bc03d6e0fb17f0e3f3e2
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>