Update libexif to 0.6.21. Add package licensing information and refresh patch.
Signed-off-by: Ian Leonard <antonlacon@gmail.com>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@40786 3c298f89-4303-0410-b956-a3cf2f4a3e73