ALSA: hda - Embed bus into controller object

... and replace with the existing hda-core helper codes.
This reduces lots of lines, finally.

Since struct hda_bus is now embedded into struct azx,
snd_hda_bus_new() is moved and expanded from hda_codec.c to
hda_controller.c, accordingly.  Also private_free bus ops and
private_data field are removed because we no longer need to point azx
object from bus (we can use container_of())

The spin locks are consolidated into the single one, bus->reg_lock.

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