dt-bindings: input: elan,ekth3000: Convert txt bindings to yaml

Convert Elan touchpad documentation to the YAML syntax.

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: David Heidelberg <david@ixit.cz>
Link: https://lore.kernel.org/r/20211009183016.65218-1-david@ixit.cz


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