ARM: dts: omap3-igep0020: add mux conf for GPIO LEDs

The IGEPv2 has a number of GPIO LED connected to OMAP
pins. Configure these pins as output GPIO.

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