* Bugfix and simplify legacy jtag-only defaulting
* Make "dummy" declare its jtag-only nature
* likewise update ft2232
* warn if selection is _required_ (multi-transport adapters),
fixes the "only ft2232 works" bug for at least dummy, with
other drivers going the "legacy" path (submit patches).
Signed-off-by: David Brownell <db@helium.(none)>