[RISCV] (sub C, (setcc x, y, eq/neq)) -> (add C-1, (setcc x, y, neq/eq)) fold for FP setcc.

This introduce an xori in some cases. I don't believe it was the
intention of the original patch. This was an accident because
nonan FP equality compares also use SETEQ/SETNE.

Also pass the correct type to getSetCCInverse.