- Convert remaining i64 custom lowering into custom instruction emission

  sequences in SPUDAGToDAGISel.cpp and SPU64InstrInfo.td, killing custom
  DAG node types as needed.
- i64 mul is now a legal instruction, but emits an instruction sequence
  that stretches tblgen and the imagination, as well as violating laws of
  several small countries and most southern US states (just kidding, but
  looking at a function with 80+ parameters is really weird and just plain
  wrong.)
- Update tests as needed.

llvm-svn: 62254