I have a a mediatek mt7925 on Arch Linux. If you check the optional dependencies for linux, wireless-reg is listed.
Install the package, and go to /etc/conf.d/wireless-regdom and uncomment the line WIRELESS_REGDOM=US. If this does not exist, write it in yourself.
However, the mediatek mt7925 should set its regdom depending on what’s going on around it, basically automatically.