libcamera: Move file_descriptor.h to base/

The FileDescriptor class is a generic helper that matches the criteria
for the base library. Move it there.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

test/file-descriptor.cpp

@@ -11,8 +11,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#include <libcamera/file_descriptor.h>
-
+#include <libcamera/base/file_descriptor.h>
 #include <libcamera/base/utils.h>
 
 #include "test.h"