ARM: davinci: da850: add mmc DT entries

Add DT entry for MMC. Also add entry for pinmux information.
Tested:
1) Without GPIO card detection and EDMA support as DT support for
   GPIO and EDMA are yet come.
2) By creating/deleting files and mounting/unmounting the partition.

Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>
Cc: linux-mmc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: davinci-linux-open-source@linux.davincidsp.com
Cc: devicetree-discuss@lists.ozlabs.org
Cc: cjb@laptop.org
Cc: Sekhar Nori <nsekhar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>