libcamera: Replace toString with operator<<() for format classes

Now that format classes implement the stream formatting operator<<(),
use it instead of the toString() function.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/cam/camera_session.cpp

@@ -145,7 +145,7 @@ void CameraSession::infoConfiguration() const
 		const StreamFormats &formats = cfg.formats();
 		for (PixelFormat pixelformat : formats.pixelformats()) {
 			std::cout << " * Pixelformat: "
-				  << pixelformat.toString() << " "
+				  << pixelformat << " "
 				  << formats.range(pixelformat).toString()
 				  << std::endl;