Enable using vector pair load/store for -mcpu=future

Enable using vector pair load/store for -mcpu=future

Late in the development of power10, we discovered that there were some issues
in using load vector pair and store vector pair instructions to do memory
copies, so the defaults were modified to not use these instructions.  This
patch re-enables using load and store vector pair instructions.

Previously the -mblock-ops-vector-pair switch was not set in POWERPC_MASKS.
This means the option was not reset if the cpu was changed via target
attributes or targt pragmas.  I added this mask to POWERPC_MASKS since the
option is set via -mcpu=future.

2024-02-15  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Turn on
	-mblock-ops-vector-pair for -mcpu=future.
	(POWERPC_MASKS): Add -mblock-ops-vector-pair.