dt-bindings: input: pwm-vibrator: Convert txt bindings to yaml

Converts txt binding to new YAML format and simplify example.

Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211208183434.98087-1-david@ixit.cz