dt-bindings: pinctrl: renesas,pfc: Document r8a779f0 support

Document Pin Function Controller (PFC) support for the Renesas R-Car
S4-8 (R8A779F0) SoC.

Signed-off-by: LUU HOAI <hoai.luu.ub@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/d51828853396773be2d6837f3301ac9da8b6f29e.1645457792.git.geert+renesas@glider.be