pinctrl: mediatek: add pinctrl-mtk-common-v2 for all MediaTek pinctrls

Irregular register arrangement and distinct logic access from various
MediaTek SoCs would cause pinctrl-mtk-common to bloat and really hard to
maintain in the future so that the patch creates pinctrl-mtk-common-v2
based on the core of mt7622-pinctrl.

The goals pinctrl-mtk-common-v2 want to achieve are to hopefully support
all of MediaTek SoCs, and two kinds of dt-bindings being supported,
Linux generic pinctrl dt-binding mt7622 supports and MediaTek per-pin
dt-binding the other SoCs support the MT8183 and MT6765 incline to make
use of.

The patch starts to refactor MT7622 pinctrl driver first with splitting
out these portable ways from there such as table-based register operation
and drive strength control that is common in both kinds of driver.

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