As both hub devices share a FuVliUsbhubDeviceClass instance we cannot 'hijack'
the vfuncs depending on object type. This allows the downstream hub to proxy to
the upstream hub where a GPIOB reset can be performed.
The USB 2.0 controller is used as a 'backup' in case the USB 3.0 firmware fails
to start. Set USB 3 hubs as a greater priority so that the USB 2 ones do not
not get added if the USB 3 firmware is working.
I misunderstood the original specification, and it seems even USB-hub-less
devices have the same header location as their "write-through" counterparts.
The logic was wrong; we should have been using command 0xB0 for attach back to
FW mode for both VL10x and VL103. Using a generic reset on VL103 always reset
the device back into bootloader mode as the ROM signatures were being written
by command 0xC0.
As now attach and detach have different code paths, there's no point having a
`FuVliDevice->reset()` vfunc, and so we can make everything a little simpler at
the same time.
To implement the SPI commands, objects can derive from FuVliDevice and
implement the new vfuncs. This allows us to override the implementation for
minor API changes.
