rs6000: Improve isel

rs6000: Improve isel

This removes output_isel.  Instead, the define_insn's now output the
isel instructions directly.

It adds a reg_or_zero operand predicate, too, because the reg_or_cint
predicate is too lax here.  Also use it in the "reversed" variants of
the instructions.

	* config/rs6000/predicates.md (zero_constant, all_ones_constant):
	Move up in file.
	(reg_or_cint_operand): Fix comment.
	(reg_or_zero_operand): New predicate.
	* config/rs6000/rs6000-protos.h (output_isel): Delete.
	* config/rs6000/rs6000.c (output_isel): Delete.
	* config/rs6000/rs6000.md (isel_signed_<mode>): Use reg_or_zero_operand
	instead of reg_or_cint_operand.  Output instruction directly (not via
	output_isel).
	(isel_unsigned_<mode>): Ditto.
	(*isel_reversed_signed_<mode>): Use reg_or_zero_operand instead of
	gpc_reg_operand.  Add an instruction alternative for this.  Output
	instruction directly.
	(*isel_reversed_unsigned_<mode>): Ditto.

From-SVN: r253665