pinctrl: rockchip: add rk3308 SoC support

This patch do support pinctrl for RK3308 SoCs.
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Link: https://lore.kernel.org/r/20191015091708.7934-3-jay.xu@rock-chips.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>