usb: phy: omap: Add omap-control Support for AM437x

This adds omap control module support for USBSS in AM437x SoC.
Update DT binding information to reflect these changes.

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