config, arm: Add an example power model

config, arm: Add an example power model

Add a script to demonstrate how power models can be wired to gem5
models. The script is meant as an example only and does not correlate
with any realistic implementation.

Change-Id: Ib95a74b2cb4af77a7816e3e8e89c89f3460775a1
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2721
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>