Checkin changes to:

1. Clean up the TargetMachine structure.  No more wierd pointers that have to
   be cast around and taken care of by the target.
2. Instruction Scheduling now takes the schedinfo as an argument.  The same
   should be done with the instinfo, it just isn't now.
3. Sparc.h is now just a factory method.  Eventually this file will dissapear,
   but probably not until we have more than one backend.  :)

llvm-svn: 564