Added submodule Xilinx Linux kernel git repository.
xylon-v2013.4-trd

Created on top of Xilinx kernel tag “xilinx-v2013.4-trd”.
Contains:
- Kernel ZC70x configuration and devicetree source files for Xylon referent
  design on HDMI output
- logiCVC framebuffer driver “xylonfb v3.0”
- logiCLK common clock framework driver “clk-logiclk v1.0”
- Driver binding documentation
- Configurable EMACPS MAC address
xylon-v2014.2-trd

Created on top of Xilinx kernel tag “xilinx-v2014.2-trd”.
Contains:
- Kernel ZC70x, ZED configuration and devicetree source files for Xylon referent
  design on HDMI output
- logiCVC framebuffer driver “xylonfb v3.0”
- logiCLK common clock framework driver “clk-logiclk v1.0”
- Driver binding documentation
- Configurable EMACPS MAC address