pinctrl: mediatek: add mtk_pctrl_spec_pull_set_samereg common code

Several mediatek soc use similar pull setting procedure as mt8173,
the pupd enable and resistance setting are in the same register.
Add common code mtk_pctrl_spec_pull_set_samereg out of spec_pull_set
in mt8173 to handle this case, so future soc driver can use it.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>