usb: dwc3_msm: Add master clock (or core clock) voting

DWC3 core requires core clock (or master clock) to run at 125MHz
in super speed mode and at >60MHz for high speed mode.
During initialization set the rate as 125MHz and later, as part of
low power mode support in the driver, clock frequency would be
changed depending on the operational mode.

Change-Id: I56f8c5d400eb9f153fa9904a35c4455618d31488
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>