ALSA: ctxfi - Clean up / optimize

- Use static tables instead of assigining each funciton pointer
- Add __devinit* to appropriate places; pcm, mixer and timer cannot be
  marked because they are kept in the function table that lives long
- Move create_alsa_devs function out of struct ct_atc to mark it
  __devinit

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