Bluetooth: btusb: Add protocol support for MediaTek MT7921U USB devices

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>