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

UPSTREAM: 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>
(cherry picked from git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl.git for-next
 commit accc1ce7d2ffc6419a8eaf8c0190d9240df0c43f)

Signed-off-by: David Wu <david.wu@rock-chips.com>
Change-Id: I940fbec4869f1395e66c8e693b838f58aa84a7a1