drm/i915: Init DDI outputs based on port_mask on skl+

Instead of listing every platform's possible DDI outputs
in intel_setup_outputs() just loop over the new port_mask
to achieve the same thing.

HSW/BDW were left as is since they still look at the straps
as well.

DSI is still a mess. For now just check for the relevant
platforms explicitly.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230616140820.11726-7-ville.syrjala@linux.intel.com