RISC-V: Add test cases for avg_floor vaadd implementation

RISC-V: Add test cases for avg_floor vaadd implementation

Add asm and run testcase for avg_floor vaadd implementation.

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

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/avg.h: New test.
	* gcc.target/riscv/rvv/autovec/avg_data.h: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i16-from-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i16-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i32-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i8-from-i16.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i8-from-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-1-i8-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i16-from-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i16-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i32-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i8-from-i16.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i8-from-i32.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_floor-run-1-i8-from-i64.c: New test.
	* gcc.target/riscv/rvv/autovec/avg_run.h: New test.

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