Kbuild warns when this file is built as a loadable module:

WARNING: modpost: missing MODULE_LICENSE() in drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.o
see include/linux/module.h for more information

Add the missing license/author/description tags.

Fixes: 8174a851 ("pinctrl: mediatek: make MediaTek pinctrl v2 driver ready for buidling loadable module")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200505140848.554957-1-arnd@arndb.deSigned-off-by: Linus Walleij <linus.walleij@linaro.org>