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.
