omap3: igep0x00: Update for DM SPL support

This change is heavily based on commit e0cc7df9 ("omap3_beagle: Update
for DM SPL support"), that did the same update for the OMAP3 Beagle board.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Enric Balletbo i Serra <eballetbo@gmail.com>