pinctrl: rockchip: Add rk3328 pinctrl support

Note, the iomux of following pins are special, need to
be recalculated specially.
 - gpio2_b4
 - gpio2_b7
 - gpio2_c7

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>