Several big changes:

Several big changes:
1. Use flags on the instructions in the .td file to indicate the PPC970 unit
   type instead of a table in the .cpp file.  Much cleaner.
2. Change the hazard recognizer to build d-groups according to the actual
   algorithm used, not my flawed understanding of it.
3. Model "must be in the first slot" and "must be the only instr in a group"
   accurately.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26719 91177308-0d34-0410-b5e6-96231b3b80d8