pinctrl: rockchip: Add iomux-route switching support for rk3399

There are 2 IP blocks pin routes need to be switched, that are
uart2dbg, pcie_clkreq.

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>