ASoC: sdm660: Make vneg_out voltage as high and add check for impedance det

Impedance headset needs higher voltage to avoid noise.
With low voltage there is THD issue on headset.
Also skip wcd_imped_config at power down
to avoid unnecessary impedance calculation.

CRs-Fixed: 2215816
Change-Id: I55258642f8c7c287dc62f854d4caac787550fbe4
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>