[RFC][DON'T MERGE] trace: energy_model: Add trace event for EM runtime modifications

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Important Note:
This is an experimental patch aiming to discuss/test the idea of
runtime modifiable EM. It tries to address the impact of static power
(leakage) change in time due to different temperature of the chip.
The purpose of sharing this patch is to get feedback from Vendors
making the real SoCs, and gather details such as:
- does it address the problem
- doesn't contain design restrictions (such as values scale, math
model),
- performs fast&smooth (lack of unacceptable delays in runtime updates)
- fits into the right running context of the EM modifier (e.g. thermal
governor, driver IRQ handler, etc)
- allows for optimizations and/or differentiation of the power vs.
  performance policy
After positive feedback and results the goal is to share this work
on the Linux Kernel Mailing List (together with justification) to
make it available in upstream/Android/production kernels.
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The Energy Model (EM) supports runtime modifications. Track the changes
in order to do post-processing analysis. Don't use arrays in the trace
event, since they are not properly supported by the tools. Instead use
simple "unroll" with emitting the trace event for each EM array entry
with proper ID information.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>