Add dt bindings for the TLV320ADCx140 Burr-Brown ADC.
The initial support is for the following:

TLV320ADC3140 - http://www.ti.com/lit/gpn/tlv320adc3140
TLV320ADC5140 - http://www.ti.com/lit/gpn/tlv320adc5140
TLV320ADC6140 - http://www.ti.com/lit/gpn/tlv320adc6140Signed-off-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20200220210759.31466-2-dmurphy@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>