This is a continuation of D47491...
POWI is an oddball math intrinsic since its 2nd argument is always a scalar integer. Add a helper function to expand STRICT_FPOWI.
Also, update the SmallVector value for both ExpandStrictFPPOWI(...) and ExpandStrictFPOp(...). The new value, 32, was chosen assuming 1024b vectors with 32b FP being the smallest element size. Special thanks to Andy for decoding how SmallVector works.