ARM: shmobile: r8a7790: Reference DMA channels in MMCIF DT nodes

ARM: shmobile: r8a7790: Reference DMA channels in MMCIF DT nodes

Add references to the transmit and receive DMA channels in the two
MMCIF nodes.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
(cherry picked from commit 108216c1e08db6c69a54ba7ee593335eceea2077)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>