ASoC: wcd9xxx: Add run-time detection of wcd9306/wcd9302

Tapan codec has two variants wcd9306 and wcd9302. Wcd9302
is derived from wcd9306 while few hardware blocks are not
available. Add support to detect the codec variant at run
time.

Change-Id: Idb5b39aec2b8262391aea475a261ee5c0fcd1ede
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>