sink: Reduce chat sink priority

sink: Reduce chat sink priority

Some gaming sound cards have custom profiles with analog-game and
analog-chat mappings that exist simultaneously. The game sink should
have higher priority than the chat sink, but currently there's no way to
affect the sink priorities from the profile-set configuration (the
mapping priority is not propagated to the sink priority).

I first thought about adding the mapping priority to the sink priority,
but that could mess up the prioritization system in
pa_device_init_priority(). I ended up checking for the intended roles
property to reduce the chat sink priority. I also reduced the iec958
priority so that the chat and iec958 sinks don't end up with the same
priority.

Fixes: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/issues/818
Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/266>