Use vector pair load/store for memcpy with -mcpu=future

Use vector pair load/store for memcpy with -mcpu=future

In the development for the power10 processor, GCC did not enable using the load
vector pair and store vector pair instructions when optimizing things like
memory copy.  This patch enables using those instructions if -mcpu=future is
used.

2024-03-22  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Enable using
	load vector pair and store vector pair instructions for memory copy
	operations.
	(POWERPC_MASKS): Make the bit for enabling using load vector pair and
	store vector pair operations set and reset when the PowerPC processor is
	changed.