rs6000: Delete the "wy" constraint

rs6000: Delete the "wy" constraint

This replaces the "wy" constraint by "wa", with isa "p8v".  It also
creates a new attribute <Fisa>, used together with all <Fv2>.

	* config/rs6000/constraints.md (define_register_constraint "wy"):
	Delete.
	* config/rs6000/rs6000.h (enum r6000_reg_class_enum): Delete
	RS6000_CONSTRAINT_wy.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Adjust.
	(rs6000_init_hard_regno_mode_ok): Adjust.
	* config/rs6000/rs6000.md: Replace "wy" constraint by "wa" with "p8v".
	Use "<Fisa>" as "isa" in all alternatives that use "<Fv2>".
	(define_mode_attr Fisa): New.
	* config/rs6000/vsx.md: Replace "wy" constraint by "wa" with "p8v".
	* doc/md.texi (Machine Constraints): Adjust.

From-SVN: r271389