[X86] Fix mul test cases in avx512-broadcast-unfold.ll to not get canonicalized to fadd. Remove the fsub test cases which were also testing fadd.
[X86] Fix mul test cases in avx512-broadcast-unfold.ll to not get canonicalized to fadd. Remove the fsub test cases which were also testing fadd.

Not sure how to prevent an fsub by constant getting turned into an fadd by negative constant.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@370515 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm