ipc4: do not declare union/structs with very generic names in headers

gateway.h defines "union flags" and "struct bits" to global namespace,
which is not good in a public interface header file. There's no functional
need to tag these struct definitions, so make the definitions
anonymous.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

src/include/ipc4/gateway.h

@@ -162,8 +162,8 @@ struct ipc4_ipc_gateway_config_blob {
 	uint32_t buffer_size;
 
 	/**< Flags */
-	union flags {
-		struct bits {
+	union {
+		struct {
 			/**< Activates high threshold notification */
 			/*!
 			 * Indicates whether notification should be sent to the host