pinctrl: mediatek: add pull related support to pinctrl-mtk-common-v2.c

Put pull control support related functions to pinctrl-mtk-common-v2.c
as these operations might be different by chips and allow different
type of driver to reuse them.

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>