drm/i915/lvds: move fitting mode from intel_lvds_connector to intel_panel

Prepare for supporting scaling mode configuration also in eDP.

Includes a drive-by-removal of an outdated comment about fitting mode.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>