cmd/compile: add AMD64 parameter register defs, Arg ops, plumb to ssa.Config

This is partial plumbing recycled from the original register abi test work;
these are the parts that translate easily.  Some other bits are deferred till
later when they are ready to be used.

For #40724.

Change-Id: Ica8c55a4526793446189725a2bc3839124feb38f
Reviewed-on: https://go-review.googlesource.com/c/go/+/260539


Trust: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>