arm64: dts: renesas: r8a77961: Add SDHI nodes

Add device nodes for the SDHI Interfaces on the Renesas R-Car M3-W+
(r8a77961) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Tested-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Link: https://lore.kernel.org/r/20191216124740.16647-7-geert+renesas@glider.be