drm/i915: Disable trickle feed for SNB/IVB cursors

We disable trickle feed whenever possible, except for the cursors
on SNB/IVB. Let's try disabling it there too if for no other reason
than consistency.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130203807.13721-5-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>