phy: omap-usb2: Adapt phy-omap-usb2 for AM437x

Adapt phy-omap-usb2 driver for AM437x.
	- Add new comaptible "ti,am437x-usb2" for AM437x
	- Pass proper data to differentiate AM437x and others.
	- AM437x doesnot support  set_vbus and start_srp.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>