usb: dwc3-msm: Add support to change USB modes using sysfs

Driver supports DRD mode and mode is changed based on
usb power_supply notification for ID and BSV changes.
This works fine for primary USB port as only one instance
of psy can exist. For other USB ports allow user to change
change modes using sysfs attribute 'mode'. This requires
user to pass qcom,psy-not-used DT attribute to handle
probe error due to duplicate registration of usb_psy.

Example commands to change the mode:
echo peripheral > /sys/devices/soc/6a00000.ssusb/mode (Device)
echo host > /sys/devices/soc/6a00000.ssusb/mode (Host)
echo none > /sys/devices/soc/6a00000.ssusb/mode (Disconnect)

Change-Id: I69b4c822d194cdd93cb77dbbf79e420bdee597d7
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>