drm/radeon: Add HD-audio component notifier support (v6)

This patch adds the support for the notification of HD-audio hotplug
via the already existing drm_audio_component framework to radeon
driver.  This allows us more reliable hotplug notification and ELD
transfer without accessing HD-audio bus; it's more efficient, and more
importantly, it works without waking up the runtime PM.

The implementation is rather simplistic: radeon driver provides the
get_eld ops for HD-audio, and it notifies the audio hotplug via
pin_eld_notify callback upon each radeon_audio_enable() call.
The pin->id is referred as the port number passed to the notifier
callback, and the corresponding connector is looked through the
encoder list in the get_eld callback in turn.

The bind and unbind callbacks handle the device-link so that it
assures the PM call order.

Also, as a gratis bonus, this patch "fixes" the regression by the
recent change in HD-audio to be more strict for the HDMI/DP
connection, too.  Since the HD-audio HDMI/DP codec requires both the
connection bit and the valid ELD to be provided, it started failing on
some RADEON gfx boards where the ELD update performed instably.  As
this change switches the communication to a direct way between the
audio and the graphics drivers, now the system receives the proper
ELD, and the HDMI/DP hotplug starts working again.

[ v2: fix the logic in radeon_audio_component_get_eld to walk the
  connector list since that is where the EDID lives and we can
  derive the encoder from the connector because the encoder has
  not been assigned at this point (i.e., during monitor probe).

  v3: the component binding is moved outside radeon_audio_init() and
  _fini(), as those are called from suspend/resume, too.
  Drop modeset lock calls that caused Oops.
  Moved Kconfig change so that it can be applied on older kernels.

  v4: revive drm_modeset_lock*() again, add the missing
  device_link_remove() call at unbinding

  v5: squash in mutex fix

  v6: squash in fix for audio get_eld callback ]

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1569
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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