ASoC: SOF: use the sof_ipc_comp reserved bytes for extended data

Use the 32bit reserved member of the struct sof_ipc_comp as the extended
data length, this will help to minimize the ABI change for adding new
extended data to the struct sof_ipc_comp, usually only minor ABI version
bump needed for every update with this new solution.

Signed-off-by: Keyon Jie <[e-mail]>
Reviewed-by: Ranjani Sridharan <[e-mail]>
Signed-off-by: Kai Vehmanen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

include/sound/sof/topology.h

···
 	uint32_t pipeline_id;
 	uint32_t core;
 
-	/* reserved for future use */
-	uint32_t reserved[1];
+	/* extended data length, 0 if no extended data */
+	uint32_t ext_data_length;
 } __packed;
 
 /*