ASoC: dt-bindings: ak5558: Add power supply property

AVDD-supply is for Analog power supply
DVDD-supply is for Digital power supply

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1598190877-9213-1-git-send-email-shengjiu.wang@nxp.com


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