ASoC: wcd934x: Add API to enable standalone micbias

Add an API in wcd934x codec driver to enable
standalone micbias. This API can be used to enable
micbias even without an active audio capture session.

CRs-fixed: 1062152
Change-Id: I98074071546c053ce3be733602adeff23d6b4b72
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>