RISC-V: Add testcases for vec_duplicate + vadd.vv combine when GR2VR cost 0

RISC-V: Add testcases for vec_duplicate + vadd.vv combine when GR2VR cost 0

Add asm dump check and run test for vec_duplicate + vadd.vv combine
to vadd.vx.  Introduce new folder to hold all related testcases.

The below test suites are passed for this patch.
* The rv64gcv fully regression test.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/rvv.exp: Add new folder vx_vf for all
	vec_dup + vv to vx testcases.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_binary.h: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_binary_data.h: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_binary_run.h: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-i16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-i8.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-1-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-i16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-i8.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx_vadd-run-1-u8.c: New test.

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