drm/i915: Stop using drm_atomic_helper_check_planes()

drm/i915: Stop using drm_atomic_helper_check_planes()

We need to insert stuff between the plane and crtc .atomic_check()
drm_atomic_helper_check_planes() doesn't allow us to do that so
stop using it and hand roll the loops instead.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190708125325.16576-9-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>