Ethernet lowrisc release

These are the pre-built executables to go with the ethernet release of the lowrisc release for the Nexys4-DDR FPGA board. It provides access to networking, remote login via ssh, compilation locally via the riscv-poky distribution, as well as improved performance with a rewritten SD-card Verilog interface and Linux driver. Remote booting and Network filing system root is offered as well as standalone use with VGA screen and USB keyboard. Admittedly performance is modest relative to a modern workstation, however many areas of optimisation are possible before commiting to a chip.