ARM: shmobile: r8a7791: Add MMCIF0 DT node

Add the MMCIF0 device to the r8a7791 device tree.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>