dt-bindings: mali-midgard: Add dynamic-power-coefficient

Add a property dynamic-power-coefficient which allows to register Energy
Model for the Mali Midgard devices.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/20201209115143.15321-2-lukasz.luba@arm.com


Signed-off-by: Rob Herring <robh@kernel.org>