pinctrl: rockchip: allow specifying the regmap location for pin-routes

Right now we expect the pin-rounting settings to be in the same area
as the iomux setting itself. And while that seems to be true for all
newer Rockchip socs, back in the wild west days of old this wasn't true.

Nowadays pin settings in the GRF normally stay in the GRF and the same
is true for pins configured from PMU registers. But old socs like the
rk3188 really sprinkle pin settings somewhat randomly through both
for its bank0.

Therefore add the option to specify a location for the route setting,
so that we can map older socs correctly. We'll keep "same" as the
default, so that we only need to specify a location in the corner-cases
described above.

Signed-off-by: Heiko Stuebner <heiko.stuebner@bq.com>
Reviewed-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>