ASoC: tlv320adcx140: Add device tree property for PDM edges

Add a device tree property to configure the PDM sampling edge for each
digital microphone.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
CC: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200514123338.20392-2-dmurphy@ti.com


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