pinctrl: rockchip: add rk3188 routes to switch between nand and emmc

The rk3188 has pins that are not handled through the regular iomuxing
for handling either nand-flash or an emmc and are set through only one
specifal setting. So utilize the routing function to simply do that
setting depending on one of the core nand/emmc signals that are actually
regular pins handled through pinctrl.

Signed-off-by: Heiko Stuebner <heiko.stuebner@bq.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>