MediaTek mt76

Driver is building locally and being tested.

LinuxKPI dependencies are being reviewed, or extracted to be finalized.

Stay tuned for more soon.

7921, 7915 and mt7996 are in the works.

• https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=273623 meta-bug for mt76. Please check there first before reporting issues.