pinctrl: rockchip: add support for multiple bank types

There are Rockchip SoCs, namely the rk3188, that combine a set of
regular banks with banks that need special handling for some settings.

Therefore add the possibility for the driver to handle more than one
bank type.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>