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/media_device/media_device_print_test.cpp

@@ -4,8 +4,8 @@
  *
  * media_device_print_test.cpp - Print out media devices
  */
-#include <iostream>
 
+#include <iostream>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>