rs6000: Fix testsuite fallout from previous fix. [PR93136]

rs6000: Fix testsuite fallout from previous fix. [PR93136]

The fix for PR target/92923 exposed some test cases with fragile
scan-assembler-times counting.  Split the test cases into smaller
functions, which allows less chance of optimizations causing slight
instruction count numbers.

gcc/testsuite/
	PR target/93136
	* gcc.dg/vmx/ops.c: Add -flax-vector-conversions to dg-options.
	* gcc.target/powerpc/vsx-vector-6.h: Split tests into smaller functions.
	* gcc.target/powerpc/vsx-vector-6.p7.c: Adjust scan-assembler-times
	regex directives.  Adjust expected instruction counts.
	* gcc.target/powerpc/vsx-vector-6.p8.c: Likewise.
	* gcc.target/powerpc/vsx-vector-6.p9.c: Likewise.