ARM: dts: omap5: enable OTG role for DWC3 controller

Since SMPS10 and OTG cable detection extcon are described here, and
work to enable OTG power when an OTG cable is plugged in, we can
define OTG mode in the controller (which is disabled by default in
omap5.dtsi).

Tested on OMAP5EVM and Pyra.

Suggested-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>