Match: Add int type fits check for form 2 of .SAT_SUB imm operand

This patch would like to add strict check for imm operand of .SAT_SUB
matching.  We have no type checking for imm operand in previous, which
may result in unexpected IL to be catched by .SAT_SUB pattern.

We leverage the int_fits_type_p here to make sure the imm operand is
a int type fits the result type of the .SAT_SUB.  For example:

Fits uint8_t:
uint8_t a;
uint8_t sum = .SAT_SUB (a, 12);
uint8_t sum = .SAT_SUB (a, 12u);
uint8_t sum = .SAT_SUB (a, 126u);
uint8_t sum = .SAT_SUB (a, 128u);
uint8_t sum = .SAT_SUB (a, 228);
uint8_t sum = .SAT_SUB (a, 223u);

Not fits uint8_t:
uint8_t a;
uint8_t sum = .SAT_SUB (a, -1);
uint8_t sum = .SAT_SUB (a, 256u);
uint8_t sum = .SAT_SUB (a, 257);

The below test suite are passed for this patch:
* The rv64gcv fully regression test.
* The x86 bootstrap test.
* The x86 fully regression test.

gcc/ChangeLog:

	* match.pd: Add int_fits_type_p check for .SAT_SUB imm operand.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/sat_arith.h: Add test helper macros.
	* gcc.target/riscv/sat_u_add_imm_type_check-57.c: New test.
	* gcc.target/riscv/sat_u_add_imm_type_check-58.c: New test.
	* gcc.target/riscv/sat_u_add_imm_type_check-59.c: New test.
	* gcc.target/riscv/sat_u_add_imm_type_check-60.c: New test.

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