LoongArch: Fix lsx-vshuf.c and lasx-xvshuf_b.c tests fail on LA664 [PR112611]

LoongArch: Fix lsx-vshuf.c and lasx-xvshuf_b.c tests fail on LA664 [PR112611]

For [x]vshuf instructions, if the index value in the selector exceeds 63, it triggers
undefined behavior on LA464, but not on LA664. To ensure compatibility of these two
tests on both LA464 and LA664, we have modified both tests to ensure that the index
value in the selector does not exceed 63.

gcc/testsuite/ChangeLog:

	PR target/112611
	* gcc.target/loongarch/vector/lasx/lasx-xvshuf_b.c: Sure index less than 64.
	* gcc.target/loongarch/vector/lsx/lsx-vshuf.c: Ditto.