hw/audio/virtio-sound: allocate an array of streams

It is much easier to migrate an array of structs than individual
structs that are accessed via a pointer to a pointer to an array
of pointers to struct.

For this reason, allocate an array of streams in
virtio_snd_realize() and initialise all stream variables that
are constant at runtime immediately after allocation.

This makes it easier to remove the virtio_snd_set_pcm_params()
and virtio_snd_pcm_prepare() calls in the realisation phase and
to migrate the audio streams of the virtio sound device after
the next few patches.

[AM: there were too many conflicts, I did `git checkout --ours -- <.>`
     and then reimplemented the patch idea
/AM]

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260803081159.91981-5-alexander@mihalicyn.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>