usb: dwc3: omap: remove x_major calculation from revision register

Remove the x_major calculation logic from the wrapper revision register
to differentiate between OMAP5 and AM437x. This was done to find the
register offsets of wrapper register. Now that We do it using dt
compatible, remove the whole logic.

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