rs6000: Fix infinite loop building ghostscript and icu [PR93658]

rs6000: Fix infinite loop building ghostscript and icu [PR93658]

Fix rs6000_legitimate_address_p(), which erroneously marks a valid Altivec
address as being invalid, which causes LRA's process_address()  to go into
an infinite loop spilling the same address over and over again.

gcc/
	PR target/93658
	* config/rs6000/rs6000.c (rs6000_legitimate_address_p): Handle VSX
	vector modes.

gcc/testsuite/
	PR target/93658
	* gcc.target/powerpc/pr93658.c: New test.