RISC-V: Adjust the vf-[378]* testcase by param=vr2fpr-cost

RISC-V: Adjust the vf-[378]* testcase by param=vr2fpr-cost

After we introduced param=vr2fpr-cost, add it to testcase to
make it happy.

	PR/target 123916

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f16.c: Add param
	vr2fpr-cost.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f32.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f64.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f16.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f32.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-7-f64.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f16.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f32.c: Ditto.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-8-f64.c: Ditto.

Signed-off-by: Pan Li <pan2.li@intel.com>