[PATCH v4] drm/i915: pass ELD to HDMI/DP audio driver

[Wu Fengguang]

Keith: this version completes the IvyBridge support :)

Bossart: hotplug is working fine now, with some minor issues:

- on G45, monitor hot removal is not handled at all in
  i915_driver_irq_handler(). I'll leave it as a future TODO.

- on IvyBridge, _repeated_ plug/unplug will trigger

  [ 1183.654859] ALSA hda_eld.c:259 HDMI: Unknown ELD version 0

  which means the ELD_valid flag will be seen by audio driver,
  however it cannot get any valid ELD data. I double checked and
  find everything in the graphics driver is working as expected:
  ironlake_write_eld() is writing the good ELD data to the same
  pipe on hot plug events. So I'll leave it as a possible bug of
  the early stage hardware.

Thanks,
Fengguang