[U-Boot] Add support to download Lattice's FPGA

This patch incorporates the Lattice's tool ispVM EMBEDDED (see http://www.latticesemi.com) to download a new bitstream to Lattice's FPGA using using the commands "fpga load" already provided by u-boot.

The file to be downloaded must be converted in binary format from the original SVF file. Documentation is provided inside the ispVM Tools.