pinctrl: mediatek: rewrite mtk_pinconf_set and related functions

pinctrl: mediatek: rewrite mtk_pinconf_set and related functions

There are many pins in a SoCs, and different pin may belong
to different "io_type", For example: some pins of MT7622 belongs
to "io_type A", the other belongs to "io_type B", and pinctrl "V0"
means handle pinconf via "io_type A" or "io_type B", so SoCs that
contain "io_type A" and "io_type B" pins, use "V0" in pinctrl driver.

This patch separates the implementation of register operations
(e.g: "bias-pull-up/down", "driving" and "input-enable") into
different functions, and lets the original V0/V1
ops to call the new functions.

Signed-off-by: Sam Shih <sam.shih@mediatek.com>