dt-bindings: input: document Goodix Berlin Touchscreen IC

Document the Goodix GT9916 wich is part of the "Berlin" serie
of Touchscreen controllers IC from Goodix.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240129-topic-goodix-berlin-upstream-initial-v15-1-6f7d096c0a0a@linaro.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>