Fix q6voiced on systemd for many devices

Turns out that the q6voiced systemd unit file expects to use /etc/conf.d/q6voiced as an environment file, while we had assumed this config was specific to openrc (/etc/conf.d/* typically is...), so this installs the config in an init-agnostic subpkg so it's available for any init system.

Thanks @Justin for figuring this out :D

Fixes #3354 (closed)

cc maintainers for devices: @caleb @joelselvaraj @TravMurav @barni2000