Move XXPERMX from altivec.md to vsx.md.

Move XXPERMX from altivec.md to vsx.md.

This patch moves the XXPERMX support from altivec.md to vsx.md.  Given
the instruction support all VSX registers, vsx.md is a more proper place
for this instruction.

In doing the move, I discovered that the xxpermx_insn used the "v"
constraint (i.e. Altivec registers), while the instruction actually
supports any VSX register, so I changed the constraint to "wa".

I also changed the register_operand to the more specific
vsx_register_operand.

I was chatting with Pat Haugen, he said that the insn type should be
"vecperm" and not "vecsimple", so I changed this as well.

gcc/
2021-04-13  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/altivec.md (UNSPEC_XXPERMX): Move to vsx.md.
	(xxpermx): Move to vsx.md.
	(xxpermx_inst): Move to vsx.md.
	* config/rs6000/vsx.md (UNSPEC_XXPERMX): Move from altivec.md.
	(xxpermx): Move from altivec.md.  Use vsx_register_operand
	instead of register_operand.  Remove setting the insn attribute
	"type" on the expander.
	(xxpermx_inst): Move from altivec.md.  Use vsx_register_operand
	instead of register_operand.  Change the constraint from "v" to
	"wa" to match the instruction.  Change insn type to vecperm.