usb: phy-msm-ssusb-qmp: Add support to set/clear PCS clamp enable reg

Clearing CLAMP_EN_B in USB3_UNI_PCS_CLAMP_ENABLE reg, clamps the PHY data
inputs and enables USB3 autonomous mode. CLAMP_EN_B is set power on default
which disables USB3 autonomous mode.

Change-Id: I6e9c4404a18e0ee2d10f1e58ccd1ca52de27e5bf
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>