This is being used for other products, e.g. USB4 docks.
If non-Intel firmware is being used (e.g. ASMedia) then the explicit
calls to `fu_intel_thunderbolt_nvm_new()` can be changed to something
like `fu_firmware_new_from_gtypes()` with all the formats listed.
Some parsers are ignoring the magic when using _FLAG_IGNORE_CHECKSUM
(which is wrong; fuzzers have no problem with enforcing a static prefix)
and other either disregard the offset or check the magic in an unsafe
way. Also, use FWUPD_ERROR_INVALID_FILE consistently for magic failure.
Add a vfunc, and move all the clever code into one place.
The signed payload attribute is currently set for devices connected through
Intel host controllers. When Thunderbolt 3 devices are connected to non-Intel
host controllers they still support signed payloads.
Update the flag accordingly in these circumstances.
Although they do a lot of the same things, trying to deal with both
kinds of device in the same GObject type was making it very hard to
understand and maintain.
Split out two GObjects that both derive from FuThunderboltDevice.
