dt-bindings: arm: Document kryo385 cpu

Document the compatible string for the Kryo385 cpus found in qualcomm
SoCs.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>