This is a step towards getting the drivers ready for new config.
Clean up namespace, remove several instances of global arrays. Instead,
use a softc to carry state around. Where possible, pass a pointer to the
softc rather than a unit number.
* Reset the card on "fresh open" as a sanity measure.
* Use the "secret bit" to enable interrupts.
* Make some parts look/behave like their cousins in dev/isa/com.c
* Set the FIFO threshold based on line speed.
* Be a little more informative when port is attached.
* Implement TIOC{G,S}FLAGS; ttyflags now works.
First two items prevent deadlock on some systems (notably the 380,
425, and 433) which some people have been reporting. Use of the
"secret bit" seems to be safe on systems which don't need it. Changes
tested on a 319, 340, 345, and 380.
thorpej