RISC-V: Add patterns for vector-scalar IEEE floating-point max

RISC-V: Add patterns for vector-scalar IEEE floating-point max

These patterns enable the combine pass (or late-combine, depending on the case)
to merge a vec_duplicate into an unspec_vfmax RTL instruction.

Before this patch, we have two instructions, e.g.:
  vfmv.v.f       v2,fa0
  vfmax.vv       v1,v2,v1

After, we get only one:
  vfmax.vf       v1,v1,fa0

In some cases, it also shaves off one vsetvli.

gcc/ChangeLog:

	* config/riscv/autovec-opt.md (*vfmin_vf_ieee_<mode>): Rename into...
	(*v<ieee_fmaxmin_op>_vf_<mode>): New pattern to combine vec_duplicate +
	vf{max,min}.vv (unspec) into vf{max,min}.vf.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vx_vf/vf-5-f16.c: Add vfmax.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-5-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-5-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-6-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-6-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-6-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f16.c: Add vfmax. Also add
	missing -fno-fast-math.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f64.c: Likewise.