Fix testcases that are raised by support -mevex512

Hi, all

This patch aims to fix some scan-asm fail of pr89229-{5,6,7}b.c since we emit
scalar vmov{s,d} here, when trying to use x/ymm 16+ w/o avx512vl but with
avx512f+evex512.

If everyone has no objection to the modification of this behavior, then we tend
to solve these failures by modifying these testcases.

BRs,
Lin

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr89229-5b.c: Modify test.
	* gcc.target/i386/pr89229-6b.c: Ditto.
	* gcc.target/i386/pr89229-7b.c: Ditto.