[AVX-512] Remove 128-bit and 256-bit masked floating point add/sub/mul/div...

[AVX-512] Remove 128-bit and 256-bit masked floating point add/sub/mul/div builtins and replace with native operations.

We can't do the 512-bit ones because they take a rounding mode argument that we can't represent.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280635 91177308-0d34-0410-b5e6-96231b3b80d8