[RISCV] Add seto pattern expansion

[RISCV] Add seto pattern expansion

Adds a `seto` pattern expansion. Without it the lowerings of `fcmp one` and
`fcmp ord` would be inefficient due to an unoptimized double negation.

Differential Revision: https://reviews.llvm.org/D59699

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357378 91177308-0d34-0410-b5e6-96231b3b80d8