drm/i915: Remove most encoder->type uses from the audio code

drm/i915: Remove most encoder->type uses from the audio code

encoder->type isn't genreally safe around DDI ports, so let's
replace some uses in the audio code with the crtc state's
output_types instead.

Actually in these cases encoder->type would work since the DP
SST case is only relevant for VLV/CHV and encoder->type==DP
is a thing on those platforms. The DP MST cases would work
as well since MST encoder->type==DP_MST always. But I think
it's best to try and minimize the encoder->type use in general
to avoid showing a bad example to people.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171030184654.17429-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>