pinctrl: rockchip: add rk3188 specifics

Besides the pull registers sitting in a separate place, the rk3188 also
has the peculiarity that the pull registers of the first bank are split
and the first half is sitting in the register space of the pmu.

Therefore this adds a special bank-type for the first bank, to handle
the two register sources.

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