pinctrl: r8a7790: add pinmux data for MMCIF and SDHI interfaces

This patch adds pinmux groups and functions for the two MMCIF and four
SDHI interfaces on r8a73a4 (APE6).

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>