pinctrl: mediatek: common-v1: Add common probe function

As a preparation to cleanup the probe mechanism of mediatek pinctrl
drivers that are using the v1 controller, add a common probe function
to this driver.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220222111144.20796-3-angelogioacchino.delregno@collabora.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>