power: Add error checking to MathExprPowerModel

MathExprPower model currently doesn't print any useful error messages
if an expression fails to evaluate. To add insult to injury, the model
only detects a failure when dumping stats and not at
initialization. This change adds a verification step in startup() that
ensures that all of the referenced stats actually exist.

Change-Id: I8f71c73341578d5882c8d93e482f5383fbda5f1d
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2661
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

style: [patch 3/22] reduce include dependencies in some headers

Used cppclean to help identify useless includes and removed them. This
involved erroneously included headers, but also cases where forward
declarations could have been used rather than a full include.

sim: Adding support for power models

This patch adds some basic support for power models in gem5.

The power interface is defined so it can interact with thermal
models as well. It implements a simple power evaluator that
can be used for simple power models that express power in the
form of a math expression. These expressions can use stats
within the same SimObject (or down its hierarchy) and some
magic variables such as "temp" for temperature.
In future patches we will extend this functionality to allow
slightly more complex expressions.

The model allows it to be extended to use other kinds of models.

Change-Id: I76752f9638b6815e229fd74cdcb7721a305cbc4b

power: Add support for power models

This patch adds some basic support for power models in gem5.

The power interface is defined so it can interact with thermal
models as well. It implements a simple power evaluator that
can be used for simple power models that express power in the
form of a math expression. These expressions can use stats
within the same SimObject (or down its hierarchy) and some
magic variables such as "temp" for temperature.
In future patches we will extend this functionality to allow
slightly more complex expressions.

The model allows it to be extended to use other kinds of models.

Finally, the thermal model is updated to use the power usage as input.