ALSA: line6: variax: Rewrite complex timer & work combo with a delayed work

Variax driver had a very complex and staged startup sequence using
multiple timers and a work.  This patch simplifies the procedure to a
single delayed work.

Now the startup stage consists of:
- VARIAX_STARTUP_VERSIONREQ:
  requesting the version and the message handler raises up to the next
  stage upon receiving the reply.  The request is repeated until a
  reply arrives.
- VARIAX_STARTUP_ACTIVATE:
  does activation, and queue for the next stage.
- VARIAX_STARTUP_SETUP:
  registers the card.

Signed-off-by: Takashi Iwai <tiwai@suse.de>