[X86][AVX] foldShuffleOfHorizOp - don't attempt to handle 256-bit X86ISD::VBROADCAST (PR49971)

NOTE: This is for the 12.x release branch ONLY

Minimal patch to avoid the issue encountered in PR49971 (it's already been dealt with in trunk through a larger refactor that can't be easily merged).

Bail for non-128-bit vector broadcasts of (F)HADD/SUB ops - the existing logic doesn't correctly deal with the fact that the broadcast will splat across the 128-bit lanes.

Reviewed By: spatel, wristow

Differential Revision: https://reviews.llvm.org/D101104