Allow splitting display.lua

[ypujante]

From this thread forum https://www.reasonstudios.com/forum/showpost.php?p=1618219&postcount=6 and @DavidAntliff response, it seems that it would be great if the re-cmake would help in doing that.

I am not sure how exactly, but that is something it would be great to have.

[ypujante]

@DavidAntliff was suggesting that this could also apply to other lua files (like motherboard_def.lua, info.lua, realtime_controller.lua, display.lua and texts.lua)

[ypujante]

Although not very fancy or flexible, but really easy to implement is to change the various (optional) single arguments to add_re_plugin, like DISPLAY_LUA, to multiple arguments and simply concatenate them in the order provided to generate the final file (and with dependencies, the file can be regenerated automatically if any of the files to concatenate changes).

ex:

add_re_plugin(
  ...
  DISPLAY_LUA ${MY_COMMON_FRAMEWORK}/src/lua/common_display.lua src/lua/display_1.lua src/lua/display_2.lua
)