usb: otg: Add support for power supply API for USB charging

With this commit, USB Driver will start using Power Supply
API rather than calling direct pmxxx driver API for USB charging.
This will allow hiding specific charger model (such as
external LTC4088 charger used for MDM9x15) from USB driver.

In case the power supply API is not support, fallback to legacy
API which uses pm8921 driver.

Change-Id: Ic0f302e3aa8aa60f6483a0fdeec9389a0ded1fac
Signed-off-by: Amit Blay <ablay@codeaurora.org>