thermal: power_allocator: Respect upper and lower bounds for cooling device

The thermal cooling device specified in DT might be instantiated for
a thermal zone trip point with a limited set of OPPs to operate on. This
configuration should be supported by Intelligent Power Allocation (IPA),
since it is a standard for other governors. Change the code and allow IPA
to get power value of lower and upper bound set for a given cooling
device.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201015112441.4056-3-lukasz.luba@arm.com