arm/dts: OMAP3: Add mmc controller nodes and board data

Add OMAP mmc related device tree data for OMAP3.
Currenly limited to only omap3-beagle board.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>