ARM: OMAP: RX-51: add missing USB phy binding

Commit 51482be9 (ARM: OMAP: USB: Add phy binding information) forgot to
add phy binding for RX-51, and as a result USB does not work anymore on
3.9-rc1. Add the missing binding.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>