dt-bindings:iio:afe:voltage-divider: txt to yaml conversion

Simple binding so straight forward conversion, though did require
adding a separate binding document for the max1027 to reflect
its abilities to provide channels to consumers.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20201031181242.742301-9-jic23@kernel.org