mt76 patches for 5.12

* add new mt7921e driver
* factor out common code shared between 7615/7663 and 7921
* performance optimizations
* 7915 dbdc fixes
* 802.11 encap offload support
* support for multiple pcie gen1 host interfaces on 7915
* 7915 testmode support
* bugfixes
* testmode support enhancements
* endian fixes
* 7915 txbf support