rs6000: ww -> wa

rs6000: ww -> wa

"ww" can always be "wa".

	* config/rs6000/constraints.md (define_register_constraint "ww"):
	Delete.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Adjust.
	(rs6000_init_hard_regno_mode_ok): Adjust.
	* config/rs6000/rs6000.h (enum r6000_reg_class_enum): Delete
	RS6000_CONSTRAINT_ww.
	* config/rs6000/rs6000.md: Adjust.
	* config/rs6000/vsx.md: Adjust.
	* doc/md.texi (Machine Constraints): Adjust.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@271932 138bc75d-0d04-0410-961f-82ee72b054a4