drm/xe: Move DSB l2 flush to a more sensible place

Flushing l2 is only needed after all data has been written.

Fixes: 01570b44 ("drm/xe/bmg: implement Wa_16023588340")
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: stable@vger.kernel.org # v6.12+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20250606104546.1996818-3-matthew.auld@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>