soundwire: bus: add bpt_stream pointer

Add a convenience pointer to the 'sdw_bus' structure. BPT is a
dedicated stream which will typically not be handled by DAIs or
dailinks. Since there's only one BPT stream per link, storing the
pointer at the link level seems rather natural.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.dev>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Liam Girdwood <liam.r.girdwood@intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Tested-by: shumingf@realtek.com
Link: https://lore.kernel.org/r/20250227140615.8147-9-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: plbossart

include/linux/soundwire/sdw.h

@@ -979,6 +979,7 @@ struct sdw_stream_runtime {
  * @stream_refcount: number of streams currently using this bus
  * @btp_stream_refcount: number of BTP streams currently using this bus (should
  * be zero or one, multiple streams per link is not supported).
+ * @bpt_stream: pointer stored to handle BTP streams.
  * @ops: Master callback ops
  * @port_ops: Master port callback ops
  * @prop: Master properties
@@ -1017,6 +1018,7 @@ struct sdw_bus {
 	struct sdw_bus_params params;
 	int stream_refcount;
 	int bpt_stream_refcount;
+	struct sdw_stream_runtime *bpt_stream;
 	const struct sdw_master_ops *ops;
 	const struct sdw_master_port_ops *port_ops;
 	struct sdw_master_prop prop;