rs6000: Delete the "wb" constraint

rs6000: Delete the "wb" constraint

This replaces the "wb" constraint by "v", with isa "p9v".

	* config/rs6000/constraints.md (define_register_constraint "wb"):
	Delete.
	* config/rs6000/rs6000.h (enum r6000_reg_class_enum): Delete
	RS6000_CONSTRAINT_wb.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Adjust.
	(rs6000_init_hard_regno_mode_ok): Adjust.
	* config/rs6000/rs6000.md: Replace "wb" constraint by "v" with "p9v".
	* config/rs6000/vsx.md: Ditto.
	* doc/md.texi (Machine Constraints): Adjust.

From-SVN: r271386