Use the new predicate support that Evan Cheng added to remove some code

Use the new predicate support that Evan Cheng added to remove some code
from the DAGToDAG cpp file.  This adds pattern support for vector and
scalar fma, which passes test/Regression/CodeGen/PowerPC/fma.ll, and
does the right thing in the presence of -disable-excess-fp-precision.

Allows us to match:
void %foo(<4 x float> * %a) {
entry:
  %tmp1 = load <4 x float> * %a;
  %tmp2 = mul <4 x float> %tmp1, %tmp1
  %tmp3 = add <4 x float> %tmp2, %tmp1
  store <4 x float> %tmp3, <4 x float> *%a
  ret void
}

As:

_foo:
        li r2, 0
        lvx v0, r2, r3
        vmaddfp v0, v0, v0, v0
        stvx v0, r2, r3
        blr

Or, with llc -disable-excess-fp-precision,

_foo:
        li r2, 0
        lvx v0, r2, r3
        vxor v1, v1, v1
        vmaddfp v1, v0, v0, v1
        vaddfp v0, v1, v0
        stvx v0, r2, r3
        blr

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24719 91177308-0d34-0410-b5e6-96231b3b80d8