The upcoming db845c doesn't have cellular modem capabilities, but still
has wifi. Avoid installing modem related configs and services by default
and only install it for devices that need it.
In SDM845, the q6voice kernel driver connects modem and audio backends.
Callaudiod seems to switch to correct audio device and prepares it, however, the audio
device get's closed since no one from the userspace is actively listening to it.
This cuts the audio in call. As a workaround, I have added to script to disable the
suspend-on-idle pulseaudio module during calls, so the audio devices don't close automatically.
Also, moving the modemmanager.conf file from the main package to the
nonfree-firmware subpackage as Modem Manager is going to work
only if the nonfree-firmwares are present.