RISC-V: Fix XPASS slp testcases

RISC-V: Fix XPASS slp testcases

This patch fixs XPASS slp testcases on trunk by
making the conditions for xfail stricter.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/partial/slp-1.c: Fix.
	* gcc.target/riscv/rvv/autovec/partial/slp-16.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-17.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-18.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-19.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-2.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-3.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-4.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-5.c: Ditto.
	* gcc.target/riscv/rvv/autovec/partial/slp-6.c: Ditto.