drm/i915: Disable trickle feed in ironlake_init_clock_gating()

We disable trickle feed in all the (relevant) clock gating functions,
except ironlake_init_clock_gating(). Copy paste the same code there as
well.

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