ASoC: wcd: add support to program button thresholds

Current software hardcodes threshold registers, due to this we can not
detect all buttons properly.So update button threshold
registers to detect buttons with different resistances.

CRs-Fixed: 662091
Change-Id: Ie487163bffbcc57dc1c0cfae78f47d4c21643c7a
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>