libcamera: Standardise on C compatibility headers

Now that our usage of C compatibility header is documented, use them
consistently through the source code.

While at it, group the C and C++ include statements as defined in the
coding style, and fix a handful of #include ordering issues.

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

test/ipa/ipa_interface_test.cpp

@@ -6,13 +6,12 @@
  */
 
 #include <fcntl.h>
+#include <iostream>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
-#include <iostream>
-
 #include <libcamera/event_dispatcher.h>
 #include <libcamera/event_notifier.h>
 #include <libcamera/timer.h>