Merge tag 'mt76-for-kvalo-2018-09-19' of https://github.com/nbd168/wireless

mt76 patches for 4.20

* lots of mt76x0 cleanups / fixes
* mt76x2u fixes
* unify code between mt76x0, mt76x2e and mt76x2u
* rename mt76x0 to mt76x0u
* improve rx buffer allocation for all variants
* prepare for adding mt76x0e (pci-e variant) support
  add CONFIG_MT76x0E kconfig symbol