RISC-V: Add testcases for vector .SAT_SUB in zip benchmark

RISC-V: Add testcases for vector .SAT_SUB in zip benchmark

This patch would like to add the test cases for the vector .SAT_SUB in
the zip benchmark.  Aka:

Form in zip benchmark:
  #define DEF_VEC_SAT_U_SUB_ZIP(T1, T2)                             \
  void __attribute__((noinline))                                    \
  vec_sat_u_sub_##T1##_##T2##_fmt_zip (T1 *x, T2 b, unsigned limit) \
  {                                                                 \
    T2 a;                                                           \
    T1 *p = x;                                                      \
    do {                                                            \
      a = *--p;                                                     \
      *p = (T1)(a >= b ? a - b : 0);                                \
    } while (--limit);                                              \
  }

DEF_VEC_SAT_U_SUB_ZIP(uint8_t, uint16_t)

vec_sat_u_sub_uint16_t_uint32_t_fmt_zip:
  ...
  vsetvli       a4,zero,e32,m1,ta,ma
  vmv.v.x       v6,a1
  vsetvli       zero,zero,e16,mf2,ta,ma
  vid.v	v2
  li            a4,-1
  vnclipu.wi    v6,v6,0   // .SAT_TRUNC
.L3:
  vle16.v       v3,0(a3)
  vrsub.vx      v5,v2,a6
  mv            a7,a4
  addw          a4,a4,t3
  vrgather.vv   v1,v3,v5
  vssubu.vv     v1,v1,v6  // .SAT_SUB
  vrgather.vv   v3,v1,v5
  vse16.v       v3,0(a3)
  sub           a3,a3,t1
  bgtu          t4,a4,.L3

Passed the rv64gcv tests.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/binop/vec_sat_arith.h: Add test
	helper macros.
	* gcc.target/riscv/rvv/autovec/binop/vec_sat_data.h: Add test
	data for .SAT_SUB in zip benchmark.
	* gcc.target/riscv/rvv/autovec/binop/vec_sat_binary_vx.h: New test.
	* gcc.target/riscv/rvv/autovec/binop/vec_sat_u_sub_zip-run.c: New test.
	* gcc.target/riscv/rvv/autovec/binop/vec_sat_u_sub_zip.c: New test.

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