ARM: dts: omap3-igep: Add USB OTG support

Commit ad871c10 ("ARM: dts: OMAP: Add usb_otg and glue data to O
added USB OTG support for most OMAP boards but some OMAP3 boards
such as IGEP boards were not updated. This patch adds an USB OTG
device node to these board.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Enric Balletbo i Serra <eballetbo@gmail.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>