dt: bindings: add binding for Allwinner A64 R_PIO pinctrl

Allwinner A64 SoC has also a dedicated pin controller for Port L GPIOs,
which is called "Port Controller (CPUs-PORT)" in SoC User Manual.

Add a binding for this pin controller, like the ones in A23/33 and H3.
Signed-off-by: NIcenowy Zheng <icenowy@aosc.xyz>
Acked-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/allwinner,sunxi-pinctrl.txt

@@ -23,6 +23,7 @@ Required properties:
   "allwinner,sun8i-h3-pinctrl"
   "allwinner,sun8i-h3-r-pinctrl"
   "allwinner,sun50i-a64-pinctrl"
+  "allwinner,sun50i-a64-r-pinctrl"
   "allwinner,sun50i-h5-pinctrl"
   "nextthing,gr8-pinctrl"