Thermal: Remove the cooling_cpufreq_list.

Problem of using this list is that the cpufreq_get_max_state callback will be
called when register cooling device by thermal_cooling_device_register, but
this list isn't ready at this moment. What's more, there is no need to maintain
such a list, we can get cpufreq_cooling_device instance by the private
thermal_cooling_device.devdata.

Signed-off-by: hongbo.zhang <hongbo.zhang@linaro.com>
Reviewed-by: Francesco Lavra <francescolavra.fl@gmail.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>