drm/i915/tv: Make TV mode autoselection actually useable

The current code insists on picking a new TV mode when
switching between component and non-component cables.
That's super annoying. Let's just keep the current TV
mode unless the new cable type actually disagrees with it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181112170000.27531-12-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>