UPSTREAM: ASoC: wm9705: add private structure

Add a private data structure. This is a preparation for a codec which
would need an another data on top of snd_ac97, which will be the case
when an MFD wm97xx device will probe wm9705.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
(cherry picked from commit c6e46e52)

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

Change-Id: I4c8d77cc5fd2c236b25b59d1154443830842a258
Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1410704


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