usb: dwc3-msm: Add support for voltage_max power supply property

Allow voltage_max property to be written from user space.  The USB
power supply input voltage can be limited by writing into
/sys/class/power_supply/usb/voltage_max sysfs file.  The user space
charger detection application uses this property value to place
an appropriate voltage request to the charger.

Change-Id: Ifefc87fb01d64850fcce6098d274e524bcaaa697
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>