lutok: new package

Lutok is a lightweight C++ API library for Lua.

https://github.com/jmmv/lutok



[Thomas:
 - move lutok inclusion in package/Config.in after including the Lua
   external modules
 - add a comment explaining why we are passing --without-atf
 - remove the logic around -ldl, it seems to build just fine without it.]

Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>