dt-bindings: qcom: Add SDM845 bindings

Add a SoC string 'sdm845' for the qualcomm SDM845 SoC

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