drm/msm/gpu: Move gpu devcore's to gpu device

The dpu devcore's are already associated with the dpu device.  So we
should associate the gpu devcore's with the gpu device, for easier
classification.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/567738/