rs6000: Delete the "wu" constraint

rs6000: Delete the "wu" constraint

This replaces the "wu" constraint by "v", with isa "p8v".  Or, in most
cases, use "wa", since the instructions allow all VSX registers, and it
does not change how GCC behaves, so it is clearer that way.

This also delete the unused <Fa>.

	* config/rs6000/constraints.md (define_register_constraint "wu"):
	Delete.
	* config/rs6000/rs6000.h (enum r6000_reg_class_enum): Delete
	RS6000_CONSTRAINT_wu.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Adjust.
	(rs6000_init_hard_regno_mode_ok): Adjust.
	* config/rs6000/rs6000.md: Replace "wu" constraint by "v" or "wa",
	both with "p8v".
	(define_mode_attr Fa): Delete.
	* config/rs6000/vsx.md: Ditto.
	* doc/md.texi (Machine Constraints): Adjust.

From-SVN: r271388