[RISCV] Make Zfh PseudoQuietFCMP definitions predicated on HasStdExtZfh

These are currently in a `Predicates = [HasStdExtZfhOrZfhmin]` block,
but Zfhmin has no fcmp instructions so the definition makes no sense for
Zfhmin.

Differential Revision: https://reviews.llvm.org/D146435