This fixes the problem when the UEFI update depends on a specific BMC
version -- including the backup BMC device means we checking that both
the primary and the backup were above a specific version.
I don't think it's ever useful to show the backup BMC device, so just
don't include it as an enumerated device.
Fixes https://github.com/fwupd/fwupd/issues/4404
Only the backup BMC device (which we ignore anyway...) can be updated
by specifying the target ID, the others need an *empty* array so that
XCC can work out what devices need to be processed.