dt-bindings:iio:adc:atmel,sama5d2-adc: txt to yaml conversion

Whilst this binding has a lot of elements they are all fairly standard.
Hence pretty much direct txt to yaml line by line conversion.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: Eugen Hristev <eugen.hristev@microchip.com>
Link: https://lore.kernel.org/r/20201031184854.745828-29-jic23@kernel.org