So there is still an open issue that has not been closed related to
what device trees should have with respect to enable-method.  There 
are 2 proposals from Mark and Arnd--

1.  Put comment in /cpus node in dts (Mark)

     ...
        cpus {
                #address-cells = <2>;
                #size-cells = <0>;

                /*
                 * We expect the enable-method to be "psci", but this is dependent on
                 * the FW, which will fill this in.
                 */

                cpu at 0 {
                        device_type = "cpu";
                        compatible = "arm,cortex-a57";
                        reg = <0x0 0x0>;
                };
     ...


2.  Put explicit psci enable-method in cpu nodes, to make it clear that psci 
    is expected.  Plus include empty psci node with a comment. (Arnd)

     ...
       /*
        * We expect the enable-method to be "psci", but this is dependent on
        * the FW, which will fill this in.
        */
        psci {
        }
     ...
        cpus {
                #address-cells = <2>;
                #size-cells = <0>;

                cpu at 0 {
                        device_type = "cpu";
                        compatible = "arm,cortex-a57";
                        reg = <0x0 0x0>;
                        enable-method = "psci";
                };
     ...


I would prefer #1.  I think putting "hints" like the psci node and
the enable-method are weak at best.  I think the comment in #1 is
enough to make the preferred approach clear.  In the end firmware will 
override the nodes and properties if it wants or needs to.

Thanks,
Stuart