pinctrl: mediatek: extend struct mtk_pin_desc which per-pin driver depends on

Because the pincrl-mtk-common.c is an implementation for per-pin binding,
its pin descriptor includes more information than pinctrl-mtk-common-v2
so far can support. So, we complement these data before writing a driver
using pincrl-mtk-common-v2.c for per-pin binding. By the way, the size of
struct mtk_pin_desc would be larger than struct pinctrl_pin_desc can hold,
so it's necessary to have a copy before the pins information is being
registered into the core.

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