Add pins, groups, and function for the MMC interface on the Renesas
R-Car S4-8 (R8A779F0) SoC.

Based on a larger patch in the BSP by LUU HOAI.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/81a35c1fac4616d25501942848eb9662d477f9ef.1645457792.git.geert+renesas@glider.be