Add get_eld audio component for i915/HD-audio
Currently, the HDMI/DP audio status and ELD are notified and obtained
via the hardware-level communication over HD-audio unsolicited event
and verbs although the graphics driver holds the exactly same
information. As we already have a notification via audio component,
this is another step forward; namely, the audio driver may fetch
directly the audio status and ELD via the new component op.
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>