MAINTAINERS: move ralink pinctrl to mediatek mips pinctrl

MAINTAINERS: move ralink pinctrl to mediatek mips pinctrl

The Ralink pinctrl driver is now under the name of MediaTek MIPS pin
controller. Move the maintainer information accordingly. Add dt-binding
schema files. Add linux-mediatek@lists.infradead.org as an associated
mailing list.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20230317213011.13656-22-arinc.unal@arinc9.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>