usb: dwc3-msm: Add support for controller power collapse

Starting from msm USB core version 1.2.0, if usb cable is
disconnected controller power collapse is allowed. Hence
add support to vote for Global Distributed Switch
Controller (GDSC) when usb cable is connected and remove
the vote when cable is disconnected to shut down the
controller power.

CRs-Fixed: 498960
Change-Id: Ia1d8bb1b8fb5370a335d28fade72485def68f80c
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>