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.

llvm-svn: 26719

llvm-svn: 26710

llvm-svn: 26608

llvm-svn: 26595

llvm-svn: 26594

llvm-svn: 26591

a nop into Freebench/neural, which speeds it up from 136->129s (~5.4%).

llvm-svn: 26590

llvm-svn: 26588

flushes

llvm-svn: 26587