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

[Stefano Babic]

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.