[X86] Remove some of the extractelts from the new MOVSS+FMA patterns.

We only need the extractelt that corresponds to the register we're trying to insert back into. We can't guarantee the others haven't been optimized out depending on how those operands were produced.

So instead just look for an FR32/FR64 input and emit a COPY_TO_REGCLASS to VR128 in the output pattern. This matches what we do for ADD/SUB/MUL/DIV.

llvm-svn: 333473