rs6000: Delete FP_ISA3

rs6000: Delete FP_ISA3

FP_ISA3 is exactly the same as SFDF, just a less obvious name.  So,
let's delete it.

2022-06-09  Segher Boessenkool  <segher@kernel.crashing.org>

	* config/rs6000/rs6000.md (FP_ISA3): Delete.
	(float<QHI:mode><FP_ISA3:mode>2): Rename to...
	(float<QHI:mode><SFDF:mode>2): ... this.  Adjust.
	(*float<QHI:mode><FP_ISA3:mode>2_internal): Rename to...
	(*float<QHI:mode><SFDF:mode>2_internal): ... this.  Adjust.
	(floatuns<QHI:mode><FP_ISA3:mode>2): Rename to...
	(floatuns<QHI:mode><SFDF:mode>2): ... this.  Adjust.
	(*floatuns<QHI:mode><FP_ISA3:mode>2_internal): Rename to...
	(*floatuns<QHI:mode><SFDF:mode>2_internal): ... this.  Adjust.