dt-bindings: at25: convert the binding document to yaml

Convert the binding document for at25 EEPROMs from txt to yaml.

Signed-off-by: Christian Eggers <ceggers@arri.de>
Link: https://lore.kernel.org/r/20200813085959.15946-1-ceggers@arri.de


Signed-off-by: Rob Herring <robh@kernel.org>