hw/virtio: add vhost-user-snd and vhost-user-snd-pci devices

hw/virtio: add vhost-user-snd and vhost-user-snd-pci devices

Tested with rust-vmm vhost-user-sound daemon:

    RUST_LOG=trace cargo run --bin vhost-user-sound -- --socket /tmp/snd.sock --backend null

Invocation:

    qemu-system-x86_64  \
            -qmp unix:./qmp-sock,server,wait=off  \
            -m 4096 \
            -numa node,memdev=mem \
            -object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on \
            -D qemu.log \
            -d guest_errors,trace:\*snd\*,trace:\*sound\*,trace:\*vhost\* \
            -chardev socket,id=vsnd,path=/tmp/snd.sock \
            -device vhost-user-snd-pci,chardev=vsnd,id=snd \
            /path/to/disk

[AJB: imported from https://github.com/epilys/qemu-virtio-snd/commit/54ae1cdd15fef2d88e9e387a175f099a38c636f4.patch]

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-Id: <20240104210945.1223134-7-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>