ALSA: hda/hdmi: add keep-alive support for ADL-P and DG2

ALSA: hda/hdmi: add keep-alive support for ADL-P and DG2

Implement HDA keep alive (KAE) support for Intel display codecs. When no
audio stream is active, the display codec will provide a continuous clock
and a valid but silent audio stream to any connected HDMI/DP receiver.
Without this, upon starting a new playback stream, initial samples may be
lost as many receivers require time to initialize for new clock.

This is a new feature in Intel AlderLake-P display codec implementation
and replaces the Intel i915 silent-stream extension that has been used
on older hardware. Main benefit of the new method is that codec no longer
needs to be kept in D0 power state.

This patch depends on commit c9365091cb12 ("drm/i915/display: program
audio CDCLK-TS for keepalives").

[ a minor coding-style fix by tiwai ]

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Jyri Sarha <jyri.sarha@intel.com>
Link: https://lore.kernel.org/r/20220216172405.3994959-1-kai.vehmanen@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>