drm/i915/audio: treat UHBR SST like MST for cpu_transcoder signalling

Both DP MST and UHBR SST require the audio component to use a real
cpu_transcoder (>= 0) value to identify the audio stream on a port.
For DP MST this was already handled; for UHBR SST it was not, causing
pin_eld_notify() to signal cpu_transcoder = -1 (the legacy SST sentinel)
and find_audio_state() to skip the per-transcoder entry for the UHBR
stream.

After suspend/resume or replug, the ELD lookup fails and audio goes
silent. Fix by detecting UHBR SST alongside DP MST when deciding
whether a real cpu_transcoder value must be used for audio state
addressing, in both the pin_eld_notify() signalling and the
find_audio_state() lookup paths.

--v2:
- Commit message and comment update. (Suraj)
- Change function name has_mst_transcoder. (Suraj)
- Avoid Live crtc access in find_audio_state. (Suraj)

--v3:
- Minor comment changes to avoid MST over 128b/132b confusion. (Suraj)

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patch.msgid.link/20260708113558.1863316-1-mitulkumar.ajitkumar.golani@intel.com

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