arm64: dts: renesas: r8a779f0: Add pinctrl device node

Add a device node for the Pin Function Controller on the Renesas R-Car
S4-8 (R8A779F0) SoC.

Note that the register block does not include registers for banks 4-7,
as they can only be accessed from the Control Domain.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/cf4d261ba1253879e117f1598b9f47798cbda635.1645458249.git.geert+renesas@glider.be