rs6000: wi->wa, wt->wa

rs6000: wi->wa, wt->wa

"wi" and "wt" mean just the same as "wa" these days.  Change them to
the simpler name.

	* config/rs6000/constraints.md (define_register_constraint "wi"):
	Delete.
	(define_register_constraint "wt"): 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_wi and RS6000_CONSTRAINT_wt.
	* config/rs6000/rs6000.md: Adjust.
	* config/rs6000/vsx.md: Adjust.
	* doc/md.texi (Machine Constraints): Adjust.

From-SVN: r271914