Add SDHI nodes to the DT of the r8a7796 SoC.

Based on the DT of the r8a7795 SoC.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>