drm/msm/dpu: remove DPU_DSPP_GC handling in dspp flush

drm/msm/dpu: remove DPU_DSPP_GC handling in dspp flush

Gamma correction blocks (GC) are not used today so lets remove
the usage of DPU_DSPP_GC in the dspp flush to make it easier
to remove GC from the catalog.

We can add this back when GC is properly supported in DPU with
one of the standard DRM properties.

changes in v3:
	- drop the link tag which was auto added before

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/534723/
Link: https://lore.kernel.org/r/20230428223646.23595-1-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>