ARM: dts: omap3: Add generic DT support for IGEP devices

Add a generic .dtsi device tree source file for the
common characteristics across IGEP Technology devices.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Acked-by: Matthias Brugger <matthias.bgg@gmail.com>
Tested-by: Enric Balletbo i Serra <eballetbo@gmail.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>