[VP][RISCV] Add vp.reduce.fmaximum/fminimum and its RISC-V codegen (#91782)

`vp.reduce.fmaximum/fminimum` are the VP version of
`vector.reduce.fmaximum/fminimum`.

GitOrigin-RevId: f8063ffe73a3a1d704b9738169bb76ebb0f8a5e0
13 files changed