ASoC: wcd934x: Add support for HPH idle detection

WCD934X audio codec supports idle detection over headphone
path to reduce power consumption when the audio signal
level is low. Add support to enable headphone idle detection
in the wcd934x codec driver.

CRs-fixed: 1066588
Change-Id: I8d67fa4055898db31b47f87b6659484aeb08f58f
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>