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.
