drm/i915: Move display w/a #1175

Move the display w/a #1175 to a better place. That place
being the new skl+ specific plane->check() hook. This leaves
the skl_check_plane_surface() stuff to deal with the gtt offset
and src coordinate stuff as originally envisioned.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907152413.15761-12-ville.syrjala@linux.intel.com