drm/msm/a6xx: Add traces for preemption

Add trace points corresponding to preemption being triggered and being
completed for latency measurement purposes.

Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8450-HDK
Signed-off-by: Antonino Maniscalco <antomani103@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/618026/


Signed-off-by: Rob Clark <robdclark@chromium.org>