libcamera: media_device: Add helper to return matching entities

Provide a helper on the MediaDevice to return a list of all
available entities which match a given function in the graph.

As a drive by, also fix a whitespace error in the documentation of
MediaDevice::setupLink.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>

include/libcamera/internal/media_device.h

@@ -55,6 +55,8 @@ public:
 
 	Signal<> disconnected;
 
+	std::vector<MediaEntity *> locateEntities(unsigned int function);
+
 protected:
 	std::string logPrefix() const override;