Add boilerplate headers comments and include guards

The initial main.cpp and libcamera.h files are missing boilerplate
header comments. libcamera.h is further missing include guards. Add
them.

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

test/init.cpp

@@ -1,3 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2018, Google Inc.
+ *
+ * init.cpp - libcamera initialization test
+ */
+
 #include <libcamera/libcamera.h>
 
 int main(void)