pinctrl: mediatek: Adjust mt8173 pinctrl kconfig

ARM64 maintainer doesn't want to add MACH_* for each SoC.
Adjust mt8173 pinctrl kconfig entry so user can manually select it.

Also make PINCTRL_MT8135 selectable when COMPILE_TEST is enabled.

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