dt-bindings:iio:potentiometer:microchip,mcp41010 txt to yaml conversion

A simple binding that I almost just move to trivial devices.
The small amount of additional documentation and relatively large number
of compatible entries convinced me to suggest we keep this one separately
documented.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Chris Coffey <cmc@babblebit.net>
Link: https://lore.kernel.org/r/20201031184854.745828-5-jic23@kernel.org