dt-bindings: mailbox: qcom-ipcc: Add compatible for SC7280

Add IPCC compatible for SC7280 SoC.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>