- Explicitly call twe_done() to poll the hardware when looping in

- Explicitly call twe_done() to poll the hardware when looping in
  twe_start() to simulate the behavior on 4.x where the driver dropped
  spl to allow interrupts to run to free up space in the command
  queue.  Be careful to only poll if we are going to make at least
  one more attempt to queue the current command.  Also, when polling,
  be careful to not call twe_startio() to queue more commands to avoid
  recursion.
- Move the buffer for formatting AEN messages into the softc instead of
  using a single driver-wide static buffer.

Requested by:	scottl (1)
Tested by:	Mike Tancsa @ Sentex