[RISCV] Add tests cases to show missed opportunity to turn vfmv.s.f into...

[RISCV] Add tests cases to show missed opportunity to turn vfmv.s.f into vmv.s.x when source is FP constant materialized in GPR.

We end up creating the constant in GPR, move to FPR, then move to vector.
We should go directly from GPR to vector.