Improve vsx_splat_<mode>_reg

Improve vsx_splat_<mode>_reg

In looking at PR target/99293, I noticed that the code in
vsx_splat_<mode>_reg used "vecmove" as the "type" insn attribute when the
"mtvsrdd" is generated.  It should use "mfvsr".  I also added a "p9v" isa
attribute for that alternative.

2022-03-23   Michael Meissner  <meissner@linux.ibm.com>

gcc/
	PR target/99392
	* config/rs6000/rs6000.md (vsx_splat_<mode>_reg): Use the correct
	insn type attribute.  Add "p9v" isa attribute as needed.