xen/sndif: Change stream's unique-id to string

Display and input protocols define "unique-id" XenBus field as string
which is much more flexible in defining unique identifiers comparing
to integer used by sound protocol. For example, this allows to provide
UUIDs as unique ID's. Align sound protocol with display and input
and redefine "unique-id" field as string.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Release-acked-by: Juergen Gross <jgross@suse.com>

xen/include/public/io/sndif.h

@@ -278,13 +278,11 @@
  *      defined under the same device.
  *
  * unique-id
- *      Values:         <uint32_t>
+ *      Values:         <string>
  *
- *      After stream initialization it is assigned a unique ID (within the front
- *      driver), so every stream of the frontend can be identified by the
- *      backend by this ID. This is not equal to stream-idx as the later is
- *      zero based within the device, but this index is contigous within the
- *      driver.
+ *      After stream initialization it is assigned a unique ID, so every
+ *      stream of the frontend can be identified by the backend by this ID.
+ *      This can be UUID or such.
  *
  *-------------------- Stream Request Transport Parameters --------------------
  *