ARM: shmobile: r8a7790 dtsi: Remove unnecessary MMC options

As of commit 423f6c2e ("mmc: sdhi: update sh_mobile_sdhi_of_data
for r8a7790"), the driver takes care of r8a7790 specific MMC options.
Hence they can be removed from the dtsi.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
[geert: Rebased, reworded, added reference]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
[simon: Rebased]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>