If we say that the version format should be the same for the `version_lowest`
and the `version_bootloader` then it does not always make sense to set it at
the same time.
Moving the `version_format` to a standalone first-class property also means it
can be typically be set in the custom device `_init()` function, which means we
don't need to worry about *changing* ther version format as set by the USB and
UDev superclass helpers.
Some plugins have devices with more than one protocol. Logically the protocol
belongs to the device, not the plugin, and in the future we could use this to
further check firmware that's about to be deployed.
This is also not exported into libfwupd (yet?) as it's remains a debug-feature
only -- protocols are not actually required for devices to be added.
