arm64: dts: qcom: sm8450 add ITS device tree node

Add device tree node corresponding to the ITS part of GICv3.

Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220502192604.272686-1-dmitry.baryshkov@linaro.org