[RISCV][GISel] Add support for G_FCMP with F and D extensions. (#70624)

We only have instructions for OEQ, OLT, and OLE. We need to convert
other comparison codes into those.

I think we'll likely want to split this up in the future to support
optimizations. Maybe do some of it in the legalizer or in a new post
legalizer lowering pass. So this patch is just enough to get something
working without adding 11 additional patterns to tablegen for each type.