sim: move bfd.h include out of sim-main.h

sim: move bfd.h include out of sim-main.h

Not all arches include this in sim-main.h, and the ones that do don't
actually use bfd defines in the sim-main.h header.  Prune it to make
sim-main.h simpler so we can kill it off entirely in the future.

We add the include to the files that utilize e.g. bfd_vma though.