dt-binding: pinctrl: berlin: document AS370 SoC pinctrl

Add as370 to existing berlin pinctrl device tree binding.
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

@@ -23,7 +23,8 @@ Required properties:
 	"marvell,berlin2q-system-pinctrl",
 	"marvell,berlin4ct-avio-pinctrl",
 	"marvell,berlin4ct-soc-pinctrl",
-	"marvell,berlin4ct-system-pinctrl"
+	"marvell,berlin4ct-system-pinctrl",
+	"syna,as370-soc-pinctrl"
 
 Required subnode-properties:
 - groups: a list of strings describing the group names.