ASoC: wcd9xxx: Enable current source support for 2nd mic detection

Use current source to detect presence of second mic if MICBIAS
for primary and secondary mic is not shared. If MICBIAS is shared,
do not use detection with current source.

Change-Id: I25009bd15cf5a593761d8b182ed4bcb6c2c210a2
Signed-off-by: Simmi Pateriya <simmip@codeaurora.org>