rs6000: Replace OPTION_MASK_DIRECT_MOVE with OPTION_MASK_P8_VECTOR [PR101865]

rs6000: Replace OPTION_MASK_DIRECT_MOVE with OPTION_MASK_P8_VECTOR [PR101865]

This is a cleanup patch in preparation to fixing the real bug in PR101865.
TARGET_DIRECT_MOVE is redundant with TARGET_P8_VECTOR, so alias it to that.
Also replace all usages of OPTION_MASK_DIRECT_MOVE with OPTION_MASK_P8_VECTOR
and delete the now dead mask.

2024-04-09  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/101865
	* config/rs6000/rs6000.h (TARGET_DIRECT_MOVE): Define.
	* config/rs6000/rs6000.cc (rs6000_option_override_internal): Replace
	OPTION_MASK_DIRECT_MOVE with OPTION_MASK_P8_VECTOR.  Delete redundant
	OPTION_MASK_DIRECT_MOVE usage.  Delete TARGET_DIRECT_MOVE dead code.
	(rs6000_opt_masks): Neuter the "direct-move" option.
	* config/rs6000/rs6000-c.cc (rs6000_target_modify_macros): Replace
	OPTION_MASK_DIRECT_MOVE with OPTION_MASK_P8_VECTOR.  Delete useless
	comment.
	* config/rs6000/rs6000-cpus.def (ISA_2_7_MASKS_SERVER): Delete
	OPTION_MASK_DIRECT_MOVE.
	(OTHER_VSX_VECTOR_MASKS): Likewise.
	(POWERPC_MASKS): Likewise.
	* config/rs6000/rs6000.opt (mdirect-move): Remove Mask and Var.