omap3: Add minimal OMAP3 IGEP module support

The OMAP3 IGEP module is a low-power, high performance production-ready
system-on-module (SOM) based on TI's OMAP3 family. More about this
board at www.igep.es.

Signed-off-by: Enric Balletbo i Serra <eballetbo@gmail.com>
[tony@atomide.com: updated for the mmc changes and to be selected by default]
Signed-off-by: Tony Lindgren <tony@atomide.com>