documentation: Add compatibles for Amlogic Meson GXBB pin controllers

Add the two new compatibles for the Amlogic Meson GXBB pin controllers.
Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

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

@@ -5,6 +5,8 @@ Required properties for the root node:
 		      "amlogic,meson8b-cbus-pinctrl"
 		      "amlogic,meson8-aobus-pinctrl"
 		      "amlogic,meson8b-aobus-pinctrl"
+		      "amlogic,meson-gxbb-periphs-pinctrl"
+		      "amlogic,meson-gxbb-aobus-pinctrl"
  - reg: address and size of registers controlling irq functionality
 
 === GPIO sub-nodes ===