[meta-xilinx] Layer Refactoring/Consolidation and MACHINE_* variables

[Nathan Rossi]

Hi All,

So I have merged the 'nrossi/layer-refactor' branch. Before doing so I did a little bit of clean up and made the MACHINE_* stuff work with the linux-yocto recipes as well as handling its use from any layer. So that means any machine that uses linux-xlnx or linux-yocto with the meta-xilinx layer can use these MACHINE_* variables.

I have also removed the existing meta-* sub-layers, so if you go to use master you will need to remove the sublayers from your bblayers.conf.

Regards,
Nathan