ARM: dts: r7s9210: Add SDHI support

Add SDHI support for the R7S9210 (RZ/A2) SoC.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>