drm/i915: Move the DSB setup/cleaup into the color code

drm/i915: Move the DSB setup/cleaup into the color code

Since the color management code is the only user of the DSB
at the moment move the DSB prepare/cleanup there too. The
code has to anyway make decisions on whether to use the DSB
or not (and how to use it). Also we'll need a place where we
actually generate the DSB command buffer ahead of time rather
than the current situation where it gets generated too late
during the mmio programming of the hardware.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221123152638.20622-9-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>