pinctrl: mediatek: add multiple register bases support to pinctrl-mtk-common-v2.c

Certain SoC own multiple register base for accessing each pin groups,
it's easy to be done with extend struct mtk_pin_field_calc to support
the kind of SoC such as MT8183.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>