qemu-keymap: Add license in generated files

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Message-Id: <20211117174533.1900570-1-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>