pinctrl: renesas: r8a77970: Share MMC pin group data

Pin groups mmc_data[14] are subsets of mmc_data8.

This reduces kernel size by 40 bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/9354645f58c12a275923046fe913cfc9602ca710.1640269757.git.geert+renesas@glider.be