LoongArch: Fix wrong code from loongarch_expand_vec_perm_1 [PR 122695]

	PR target/122695

gcc/

	* config/loongarch/loongarch.cc (loongarch_expand_vec_perm_1):
	Simplify and fix the logic preventing the xvshuf.* unpredictable
	behavior.

gcc/testsuite/

	* gcc.target/loongarch/pr122695-1.c: New test.
	* gcc.target/loongarch/pr122695-2.c: New test.

(cherry picked from commit f168d62bc552176572832bf129c9b392aeff46ad)
3 files changed