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/buffer.cpp

@@ -5,13 +5,13 @@
  * buffer.cpp - Buffer handling
  */
 
+#include <libcamera/buffer.h>
+
 #include <errno.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <unistd.h>
 
-#include <libcamera/buffer.h>
-
 #include "log.h"
 
 /**