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>

test/process/meson.build

@@ -6,7 +6,7 @@ process_tests = [
 
 foreach t : process_tests
     exe = executable(t[0], t[1],
-                     dependencies : libcamera_dep,
+                     dependencies : libcamera_private,
                      link_with : test_libraries,
                      include_directories : test_includes_internal)