arm64: dts: renesas: r8a779g0: Add pinctrl device node

Add a device node for the Pin Function Controller on the Renesas R-Car
V4H (R8A779G0) SoC.

Based on a larger patch in the BSP by Takeshi Kihara.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/ecddcadd2fad46b1cf4c9be3ec750f360b9730e4.1662715538.git.geert+renesas@glider.be