ASoC: dt-bindings: wcd938x: Add mic bias supply property

Add vdd mic bias supply, which is required to provide bias
for wcd938x codec.

Signed-off-by: Srinivasa Rao Mandadapu <quic_srivasam@quicinc.com>
Co-developed-by: Venkata Prasad Potturu <quic_potturu@quicinc.com>
Signed-off-by: Venkata Prasad Potturu <quic_potturu@quicinc.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1647852981-27895-3-git-send-email-quic_srivasam@quicinc.com


Signed-off-by: Mark Brown <broonie@kernel.org>