pinctrl: sh-pfc: r8a7791: Add ADI pinconf support

Add pin configuration support for Gyro-ADC, named ADI on r8a7791 SoC.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Tested-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>