drm/i915/skl: Query display address through a wrapper

Need to do this in order to support 90/270 rotated display.

v2: Pass in drm_plane instead of plane index to intel_obj_display_address.

v3:
    * Renamed intel_obj_display_address to intel_plane_obj_offset.
      (Chris Wilson)
    * Simplified rotation check to bitwise AND. (Chris Wilson)

v4:
    * Extracted 90/270 rotation check into a helper function. (Michel Thierry)

v5:
    * Rebased for ggtt view changes.

For: VIZ-4545
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>