drm/i915: move and group fdi members under display.fdi

Move display fdi related members under drm_i915_private display
sub-struct.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b66fe7cf2c6f9e5b7bbfcaff40400492ac706721.1661779055.git.jani.nikula@intel.com