arm64: dts: qcom: add sm8250 GPU nodes

This brings up the GPU. Tested on HDK865 by running vulkan CTS.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20200709135251.643-15-jonathan@marek.ca


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>