documentation: Add compatibles for Amlogic Meson AXG pin controllers

Add compatibles for Amlogic Meson AXG pin controllers
Reviewed-by: NNeil Armstrong <narmstrong@baylibre.com>
Acked-by: Rob Herring <robh at kernel.org>
Signed-off-by: NXingyu Chen <xingyu.chen@amlogic.com>
Signed-off-by: NYixun Lan <yixun.lan@amlogic.com>
Signed-off-by: NKevin Hilman <khilman@baylibre.com>

Documentation/devicetree/bindings/pinctrl/meson,pinctrl.txt

@@ -9,6 +9,8 @@ Required properties for the root node:
 		      "amlogic,meson-gxbb-aobus-pinctrl"
 		      "amlogic,meson-gxl-periphs-pinctrl"
 		      "amlogic,meson-gxl-aobus-pinctrl"
+		      "amlogic,meson-axg-periphs-pinctrl"
+		      "amlogic,meson-axg-aobus-pinctrl"
  - reg: address and size of registers controlling irq functionality
 
 === GPIO sub-nodes ===