Instead of allocating snd_intelhad struct, use the card's private_data
and embed it.  It simplifies the code a lot.

While we're at it, embed had_stream into snd_intelhad struct instead
of individually allocating, and rename had_pvt_data to a bit more
specific name, had_stream_data.
Signed-off-by: Takashi Iwai <tiwai@suse.de>