mmc: sdhi: update sh_mobile_sdhi_of_data for r8a7778

This patch updates r8a7778 DT data to have SoC specific settings.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Chris Ball <chris@printf.net>