Tinyalsa is an Android library, very rarely packaged by traditional
Linux distributions. It can easily be replaced with the more usual
`libasound` in this case, which will make packaging it easier.

To ease packaging q6voiced for distributions

Signed-off-by: Manuel Traut <manut@mecka.net>

The daemon listens for both.

q6voiced expects 2 variables in its OpenRC file to specify
the card and device IDs of the modem audio device, document this.

https://github.com/tinyalsa/tinyalsa/commit/855354a87d2983e190088bc5330c129094b900ca
changed the pcm_open() call in tinyalsa to not automatically call pcm_prepare().
Now we need to do that explicitly in q6voiced to ensure that the audio streams
are actually being started. Otherwise q6voiced won't really do anything.

ModemManager can also start calls now, listen for its DBUS signals
as well to start q6voice when necessary.

Note: Unlike for oFono, call objects may be added long before actually
starting the call. Therefore we listen for StateChanged signals instead.

linux-postmarketos-qcom-msm8916 now supports voice call audio.
However, at the moment the audio stream needs to be explicitly started
by opening some PCM audio devices when the call is started
(even though no audio data is written to the PCM device).

Eventually this should go away by implementing codec2codec support
for q6voice in the kernel. In that case, the stream would be started
once the audio routes are set up using ALSA UCM. However, this is a bit
complicated actually so for now it's nice to have a workaround:

q6voiced listens on dbus for signals from oFono, and opens/closes the
PCM device when a call is initiated/ended in oFono. This essentially
makes voice call audio work out of the box (provided that the audio
routing, e.g. Earpiece and a microphone is set up appropriately).

Co-Authored-By: Nikita Travkin <nikitos.tr@gmail.com>