drm/i915/display: Move display device info to header under display/

Moving display-specific substructure definitions will help keep display
more self-contained and make it easier to re-use in other drivers (i.e.,
Xe) in the future.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230523195609.73627-2-matthew.d.roper@intel.com