UPSTREAM: ALSA: ac97: add an ac97 bus

AC97 is a bus for sound usage. It enables for a AC97 AC-Link to link one
controller to 0 to 4 AC97 codecs.

The goal of this new implementation is to implement a device/driver
model for AC97, with an automatic scan of the bus and automatic
discovery of AC97 codec devices.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
(cherry picked from commit 74426fbf)

BUG=b:110025789
TEST=Test Audio use cases with full SOF 0.6 rebase release series applied.

Change-Id: I7f4d622200c8a798bc2282cb197a97a2eef16d19
Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1410696


Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Kamal Ap <kamal.ap@intel.com>