[X86] Split masked instruction tests to enable D60940.

We need to split tests that rely on isel duplicating operations
for different masking conditions. Repeating the operation is
more costly than emitting the masking separately.

The change here is a mechanical splitting of tests that
call multiple intrinsics in one function into separate
functions that call one intrinsic. We could obviously avoid
the splitting by giving the intrinsics different operands, but
that would need closer scrutiny than just splitting.