conf: Introduce support for virtio-sound devices

conf: Introduce support for virtio-sound devices

This patch adds parsing of the virtio sound model, along with parsing
of virtio options and PCI/virtio-mmio address assignment.

A new 'streams' attribute is added for configuring number of PCM streams
(default is 2) in virtio sound devices. QEMU additionally has jacks and chmaps
parameters but these are currently stubbed, hence they are excluded in this
patch series.

Signed-off-by: Rayhan Faizel <rayhan.faizel@gmail.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>