The docs say that the trickle feed disable bit is present (for primary
planes only, not video sprites) on CTG, and that it must be set
for ELK. Just set it for all g4x chipsets.

v2: Do it in init_clock_gating too
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>