drm/i915/sdvo: Utilize intel_panel for fixed_mode

Remove the local lvds fixed mode pointer from the sdvo encoder
structure and instead utilize intel_panel like everyone else.

v2: intel_sdvo_destroy() is gone

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180917151504.8754-2-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>