ASoC: wcd: add support to configure hs_vref

hs_vref is reference voltage used to judge type of cable inserted,
this voltage need to be changed depending on the headset
chracteristics. So add support to configure hs_vref.

Change-Id: I98c545f0c9b20f0137fe924fd464bdcc791ea205
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>