Documentation: devicetree: arm: cpus/cpu nodes bindings updates

In order to extend the current cpu nodes bindings to newer CPUs
inclusive of AArch64 and to update support for older ARM CPUs this
patch updates device tree documentation for the cpu nodes bindings.

Main changes:
    - adds 64-bit bindings
    - define usage of #address-cells
    - defines behaviour on pre and post v7 uniprocessor systems
    - adds ARM 11MPcore specific reg property definition
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>