pinctrl: ralink: move to mediatek as mtmips

This platform from Ralink was acquired by MediaTek in 2011. Then, MediaTek
introduced new SoCs which utilise this platform. Move the driver to
mediatek pinctrl directory. Rename the ralink core driver to mtmips.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20230317213011.13656-5-arinc.unal@arinc9.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>