RISC-V: Add test case of unsigned scalar SAT_MUL form 5 for mul

RISC-V: Add test case of unsigned scalar SAT_MUL form 5 for mul

Add test case for both the run and asm check of mul based SAT_MUL.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/sat/sat_u_mul-6-u16-from-u32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u16-from-u64.rv32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u16-from-u64.rv64.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u32-from-u64.rv32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u32-from-u64.rv64.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u8-from-u16.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u8-from-u32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u8-from-u64.rv32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-6-u8-from-u64.rv64.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u16-from-u32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u16-from-u64.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u32-from-u64.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u8-from-u16.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u8-from-u32.c: New test.
	* gcc.target/riscv/sat/sat_u_mul-run-6-u8-from-u64.c: New test.

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