conf: vc4-hdmi: use a proper hdmi pcm, fix broken default pcm

conf: vc4-hdmi: use a proper hdmi pcm, fix broken default pcm

Userspace expects to see a HDMI pcm, so remove the somewhat broken
front and iec958 pcms and add a proper hdmi pcm instead.

The hdmi pcm supports HD/HBR audio passthrough and relays the IEC958
status bits on to the kernel driver so it can switch to HBR audio
packets if needed. The control hook is marked optional because kernels
before 5.14 didn't expose the IEC958 controls.

The default pcm never worked as dmix doesn't support the iec958 format.
So drop dmix, only use plug and softvol, and use the hdmi pcm for
iec958 formatting.

Fixes: https://github.com/alsa-project/alsa-lib/issues/229
Link: https://lore.kernel.org/alsa-devel/20220430142845.229409-1-hias@horus.com/
Signed-off-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>