buildroot

luarocks: move the option --deps-mode

The option moves from `luarocks make` command to the LuaRocks config file.

This change and the merge of PR https://github.com/keplerproject/luarocks/pull/236
in LuaRocks 2.2.0 avoids the confusing message "Missing dependency"

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>