dt-bindings: input: gpio-keys: reference input.yaml and document properties

The original text bindings documented "autorepeat" and "label"
properties (in the device node, beside the nodes with keys).  DTS use
also poll-interval.  Reference the input.yaml to get these top-level
properties.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220705120356.94876-3-krzysztof.kozlowski@linaro.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>