lua-sdl2: refactor with cmake

that allows optional dependencies

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
[Thomas:
 - use "luainterpreter" instead of "lua" in the dependencies
 - replace with a Git formatted patch that doesn't comment code but
   removes it.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>