drm/i915/skl: Support secondary (rotated) frame buffer... addresses. (Daniel Vetter) ...view for display. (Ville Syrjälä, Daniel Vetter) ...work has been extracted out. (Daniel Vetter) ...implementation into i915_gem_gtt.c (Daniel Vetter) Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>