usb: dwc3: omap: initialize the register offset values for omap5 and AM437x

This patch Initializes the register offset values depending
on the X_MAJOR of USBOTGSS_REVISION register. Also adds register
offset defines and new debug register defines.

X_MAJOR is 2 for both OMAP5 and AM437x. But both have different
glue register layout. Differentiate AM437x using dt compatible.

Register offsets are cached in dwc3_omap struct for reg reads
and writes.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>