There is mt7921 firmware download mechanism

1. Read Chip id from MT7921.

2. Download firmware by endpoint 0, it's the same mechanism with
mt7663/mt7668.
   (it's medaitek specific header format for downloading firmware.)

3. Enabling Bluetooth function.

The information in /sys/kernel/debug/usb/devices about the MT7921U
Bluetooth device is listed as the below.

  T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 40 Spd=480  MxCh= 0
  D:  Ver= 2.10 Cls=ef(misc ) Sub=02 Prot=01 MxPS=64 #Cfgs=  1
  P:  Vendor=0e8d ProdID=7961 Rev= 1.00
  S:  Manufacturer=MediaTek Inc.
  S:  Product=Wireless_Device
  S:  SerialNumber=000000000
  C:* #Ifs= 3 Cfg#= 1 Atr=e0 MxPwr=100mA
  A:  FirstIf#= 0 IfCount= 3 Cls=e0(wlcon) Sub=01 Prot=01
  I:* If#= 0 Alt= 0 #EPs= 3 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=125us
  E:  Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
  E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
  I:* If#= 1 Alt= 0 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=   0 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=   0 Ivl=1ms
  I:  If#= 1 Alt= 1 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=   9 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=   9 Ivl=1ms
  I:  If#= 1 Alt= 2 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=  17 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=  17 Ivl=1ms
  I:  If#= 1 Alt= 3 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=  25 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=  25 Ivl=1ms
  I:  If#= 1 Alt= 4 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=  33 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=  33 Ivl=1ms
  I:  If#= 1 Alt= 5 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=  49 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=  49 Ivl=1ms
  I:  If#= 1 Alt= 6 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=btusb
  E:  Ad=83(I) Atr=01(Isoc) MxPS=  63 Ivl=1ms
  E:  Ad=03(O) Atr=01(Isoc) MxPS=  63 Ivl=1ms
  I:* If#= 2 Alt= 0 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=(none)
  E:  Ad=8a(I) Atr=03(Int.) MxPS=  64 Ivl=125us
  E:  Ad=0a(O) Atr=03(Int.) MxPS=  64 Ivl=125us
  I:  If#= 2 Alt= 1 #EPs= 2 Cls=e0(wlcon) Sub=01 Prot=01 Driver=(none)
  E:  Ad=8a(I) Atr=03(Int.) MxPS= 512 Ivl=125us
  E:  Ad=0a(O) Atr=03(Int.) MxPS= 512 Ivl=125us
Signed-off-by: Mark Chen <Mark-YW.Chen@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>