make.py: add clean action
software/bios/Makefile: do not use mkmscimg on windows platforms for now
use bitstream_ext from platform & add USBBlaster programmer
targets/simple.py: add SimpleSoCAltera for de0nano and rename SimpleSoC to SimpleSoCXilinx
gensoc: create PowerUpRst class and use it in simple
bios: compute crc32 in python instead of using mkmscimg since it was not portable on windows
programmer: clean up
de0nano : integrate c4sdrphy and move s6ddrphy to sdramphy