Treat soft-float as unsupported for fast-isel. Additionally, ensure we check
that lowering f32 arguments also considers the case of soft-float mode.
We should check UnsupportedFPMode instead of useSoftFloat in order to be consistent with similar tests in other places.
FastISel is not enabled for microMIPS as we haven't test this configuration. Also, try to enable FastISel by using -O0 and -relocation-model=pic as we do on (hopefully most of) the other tests.