libcamera: stream: Add operator<<() to print StreamRole as a string

libcamera prints stream role values in log messages. To be more
user-friendly, add a specialization of operator<<() to print the role
name as a string instead of a numerical value.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/stream.h

@@ -9,6 +9,7 @@
 
 #include <map>
 #include <memory>
+#include <ostream>
 #include <string>
 #include <vector>
 
@@ -70,6 +71,8 @@ enum StreamRole {
 
 using StreamRoles = std::vector<StreamRole>;
 
+std::ostream &operator<<(std::ostream &out, StreamRole role);
+
 class Stream
 {
 public: