libcamera: Include header related to source file first

Include the header file corresponding to the source file in the very
first position. This complies with the Google C++ coding style
guideliens, and helps ensuring that the headers are self-contained.

Three bugs are already caught by this change (missing includes or
forward declarations) in device_enumerator.h, event_dispatcher_poll.h
and pipeline_handler.h. Fix them.

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

src/libcamera/timer.cpp

@@ -5,11 +5,12 @@
  * timer.cpp - Generic timer
  */
 
+#include <libcamera/timer.h>
+
 #include <time.h>
 
 #include <libcamera/camera_manager.h>
 #include <libcamera/event_dispatcher.h>
-#include <libcamera/timer.h>
 
 #include "log.h"