Improve up AMP definition
Improve up AMP definition

In the old definition, which states that CPUs just need to be running
different "Tasks" is loose, and could apply to an SMP system, depending
on how you interpret the word task.

Signed-off-by: Charles Garcia-Tobin <ca20920a359f8aa1bb4691e7bf83df477b76bdc9@arm.com>
Signed-off-by: Grant Likely <9069e6f5a2b566e2674a0ba1e2bf39c12c195fad@linaro.org>

devicetree-org/devicetree-specification,kvekaria/devicetree-specification