Initial import of Ralink/Mediatek MIPS SoC support #7

[sgalabov]

Summary

GPIO controller drivers import.

As with other Ralink/Mediatek work, there are 2 versions of the GPIO controller driver, depending on the type of SoC.
This revision introduces initial support for these.

[adrian]

sys/mips/mediatek/mtk_gpio_v1.c

457 ↗

(On Diff #14990)

ok, so as long as the pin can't change input<->output during runtime, then yeah, we don't have to protect it by a lock!