RISC-V: Add fminimumnum and fmaximumnum support (#104411)
Since 2.2, `fmin.s/fmax.s` instructions follow the IEEE754-2019, if F
extension is avaiable; and `fmin.d/fmax.d` also follow the IEEE754-2019
if D extension is avaiable.
So, let's mark them as Legal.
