ASoC: wcd9335: Define callback function for hph pull down

Define callback function to control headphone auto
pull down for wcd9335. It is required for mbhc to
disable/enable the pull down on headphone when plug
detection is in progress.

Change-Id: I63774a9187124ea69a2baff9099102348d719c52
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>