pinctrl: mediatek: Use real dependencies

Do not hide pinctrl drivers for Mediatek platforms using
conditionals. Doing so actually leaves the symbols present (but
always disabled) on all other platforms, which is confusing and
inefficient. Better use real dependencies so that the symbols do not
exist at all on platforms where they are not relevant.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reported-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>