usb: dwc3-msm: Disable clock gating always

There is a known HW bug on the DWC3 MSM implementation that
causes the internal RAM clock to get stuck when entering low
power modes. The workaround for this is to disable internal
clock gating always. As the DWC3_GCTL register will get reset
when coming out of power collapse, make sure to save and
restore the value during suspend and resume.

Change-Id: Id5c7496fbc65f328c84e63bb0588c91fb226c1d7
Signed-off-by: Jack Pham <jackp@codeaurora.org>