usb: dwc3-msm: Request for otg_interrupt irq

DWC3 has separate irq line for OTG interrupts (e.g. ID / BSV).
These interrupts are needed to detect cable connect and disconnect
events. Hence, request for this interrupt line from OTG driver.
Also, update device tree binding documentation for DWC3 core.

Change-Id: Ie97e4b3b5dcf840eabeb01b5c5d6531a8a70a3c9
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>