ARM: dts: dra7: Use "ti,dra7x-usb2-phy2" compatible string for USB2 PHY2

The USB2 PHY2 has a different register map compared to USB2 PHY1
to power on/off the PHY. In order to handle it, use the new compatible
string "ti,dra7x-usb2-phy2" for the second instance of USB2 PHY.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>