ASoC: wcd934x: Fix mbhc errors upon removing SND_SOC_WCD934X_MBHC

Fix any mbhc related error seen in code compilation
when SND_SOC_WCD934X_MBHC is removed in Kconfig for
disabling mbhc. Add stub inline functions for any mbhc
function when SND_SOC_WCD934X_MBHC is not defined.

CRs-fixed: 2006189
Change-Id: I7222df8cd59ff751bf2109430ce0a0a496a76eb9
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>