[RISCV] Add intrinsics for vfmv.f.s and vfmv.s.f

Similar to D93365, but for floating point. No need for special ISD opcodes
though. We can directly isel these from intrinsics. I had to use anyfloat_ty
instead of anyvector_ty in the intrinsics to make LLVMVectorElementType not
crash when imported into the -gen-dag-isel tablegen backend.

Differential Revision: https://reviews.llvm.org/D93426