USB: dwc3-msm: Add support for PMIC VBUS notifications

Currently depending on PHY for VBUS notifications for USB
cable connect/disconnect. This could cause some power
consumption as LDOs should be enabled for HV interrupt for
VBUS to be triggered by PHY. Hence register power supply for
USB for getting VBUS notifications from PMIC so that USB can
enter deep power saving mode.

Change-Id: Ic4c9fa0245f88cdba50ca277215618ab3bf36cf9
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>