drm/i915: Move cached EDID to intel_connector

Move the cached EDID from intel_dp and intel_lvds_connector to
intel_connector. Unify cached EDID handling for LVDS and eDP, in
preparation for adding more generic EDID caching later.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>