rs6000: Use iterators in more DFP patterns

rs6000: Use iterators in more DFP patterns

I noticed some patterns in dfp.md could use the D64_D128 iterator but
don't yet.  This converts all remaining simple cases.

	* config/rs6000/dfp.md (D64_D128): Move earlier in the file.
	(dfp_suffix): Ditto.
	(adddd3, addtd3): Merge to ...
	(add<mode>3 for D64_D128): ... this.
	(subdd3, subtd3): Merge to ...
	(sub<mode>3 for D64_D128): ... this.
	(muldd3, multd3): Merge to ...
	(mul<mode>3 for D64_D128): ... this.
	(divdd3, divtd3): Merge to ...
	(div<mode>3 for D64_D128): ... this.
	(*cmpdd_internal1, *cmptd_internal1): Merge to ...
	(*cmp<mode>_internal1 for D64_D128): ... this.
	(ftruncdd2, ftrunctd2): Merge to ...
	(ftrunc<mode>2 for D64_D128): ... this.
	(fixdddi2, fixtddi2): Merge to ...
	(fix<mode>di2 for D64_D128): ... this.

From-SVN: r274217