pinctrl: rockchip: add support for the rk3399

The pinctrl of rk3399 is much different from other's,
especially the 3bits of drive strength.
Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

@@ -22,7 +22,7 @@ Required properties for iomux controller:
   - compatible: one of "rockchip,rk2928-pinctrl", "rockchip,rk3066a-pinctrl"
 		       "rockchip,rk3066b-pinctrl", "rockchip,rk3188-pinctrl"
 		       "rockchip,rk3228-pinctrl", "rockchip,rk3288-pinctrl"
-		       "rockchip,rk3368-pinctrl"
+		       "rockchip,rk3368-pinctrl", "rockchip,rk3399-pinctrl"
   - rockchip,grf: phandle referencing a syscon providing the
 	 "general register files"