RISC-V: Add testcases for unsigned imm vec SAT_SUB form2~4

Form2:
void __attribute__((noinline))             \
vec_sat_u_sub_imm##IMM##_##T##_fmt_2 (T *out, T *in, unsigned limit)  \
{                                                   \
  unsigned i;                                       \
  for (i = 0; i < limit; i++)                       \
    out[i] = in[i] >= (T)IMM ? in[i] - (T)IMM : 0;  \
}

Form3:
void __attribute__((noinline))             \
vec_sat_u_sub_imm##IMM##_##T##_fmt_3 (T *out, T *in, unsigned limit)  \
{                                                   \
  unsigned i;                                       \
  for (i = 0; i < limit; i++)                       \
    out[i] = (T)IMM > in[i] ? (T)IMM - in[i] : 0;   \
}

Form4:
void __attribute__((noinline))             \
vec_sat_u_sub_imm##IMM##_##T##_fmt_4 (T *out, T *in, unsigned limit)  \
{                                                   \
  unsigned i;                                       \
  for (i = 0; i < limit; i++)                       \
    out[i] = in[i] > (T)IMM ? in[i] - (T)IMM : 0;   \
}

Passed the rv64gcv full regression test.

Signed-off-by: Li Xu <xuli1@eswincomputing.com>

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/sat/vec_sat_arith.h: add unsigned imm vec sat_sub form2~4.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_data.h: add data for vec sat_sub.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-2-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-2-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-2-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-2-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-3-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-3-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-3-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-3-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-4-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-4-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-4-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-4-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-2-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-2-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-2-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-2-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-3-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-3-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-3-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-3-u8.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-4-u16.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-4-u32.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-4-u64.c: New test.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_imm-run-4-u8.c: New test.