usb: musb: dsps: dt binding - add resources, example

OMAP2+ family of devices are now obtaining resources via DT, earlier
it was obtained from hwmod. Update binding document accrodingly, while
at it add example.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>