virtio-sound: add latency_bytes definition

[MatiasVara]

Section 5.14.6.8 PCM I/O Messages defines the latency_bytes field that is used by the device to inform the driver the latency in terms of bytes until a buffer is played or has been captured. However, the specification does not describe this mechanism very well. We propose to improve the existing description with a better one based on the comment at https://github.com/google/crosvm/blob/main/common/audio_streams/src/audio_streams.rs#L380C9-L380C96 and the discussion we had at https://lore.kernel.org/all/ZR6EzpQb6J1TxbM8@fedora/T/.

Fix: https://lore.kernel.org/virtio-comment/Zky3vZU+P37H4VPb@fedora/

[mstsirkin]

@MatiasVara please edit the issue to add a bit more detail:

• include description of the issue
• include short summary of the proposal

[MatiasVara]

@MatiasVara please edit the issue to add a bit more detail:

• include description of the issue
• include short summary of the proposal

Hello @mstsirkin I just updated the description.