libcamera: Correct struct forward declarations

Several structures are forward-declarated as classes. Fix this by using
the struct keyword where appropriate, or removing the forward
declaration when not needed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/camera.h

@@ -21,9 +21,10 @@ class Buffer;
 class PipelineHandler;
 class Request;
 class Stream;
-class StreamConfiguration;
 class StreamUsage;
 
+struct StreamConfiguration;
+
 class CameraConfiguration
 {
 public:

src/libcamera/include/camera_sensor.h

@@ -18,7 +18,8 @@ namespace libcamera {
 
 class MediaEntity;
 class V4L2Subdevice;
-class V4L2SubdeviceFormat;
+
+struct V4L2SubdeviceFormat;
 
 class CameraSensor : protected Loggable
 {

src/libcamera/include/pipeline_handler.h

@@ -26,7 +26,6 @@ class MediaDevice;
 class PipelineHandler;
 class Request;
 class Stream;
-class StreamConfiguration;
 class StreamUsage;
 
 class CameraData