libcamera/base: Validate internal headers as private

Headers which must not be exposed as part of the public libcamera API
should include base/private.h.

Any interface which includes the private.h header will only be able to
build if the libcamera_private dependency is used (or the
libcamera_base_private dependency directly).

Build targets which are intended to use the private API's will use the
libcamera_private to handle the automatic definition of the inclusion
guard.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/base/utils.h

@@ -19,6 +19,8 @@
 #include <utility>
 #include <vector>
 
+#include <libcamera/base/private.h>
+
 #ifndef __DOXYGEN__
 
 /* uClibc and uClibc-ng don't provide O_TMPFILE */