The igen tool sets up the SD & CPU defines for code fragments to use,
but v850 was expecting "sd". Change all the igen related code to use
SD so it actually compiles, and fix a few places to use "CPU" instead
of hardcoding cpu0.
Rename v850_sim.h to v850-sim.h to match other ports, and move most
of the arch-specific content out of sim-main.h to it. This isn't a
big win though as we still have to include the header in sim-main.h
due to the igen interface: it hardcodes including sim-main.h in its
files. So until we can fix that, we have to keep bleeding these
settings into the common codes.
