drm/i915: Fix has_audio readout for DDI A

Transcoder EDP does not support audio. Let's not try to
read the state of the audio enable bit HSW_AUD_PIN_ELD_CP_VLD
based on the pipe when using transcoder EDP.

While at it make the function static and flatten it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171129164303.18793-3-ville.syrjala@linux.intel.com


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>