thermal: convert cpu_cooling to use an IDA

thermal cpu cooling does not use the ability to look up pointers by ID,
so convert it from using an IDR to the more space-efficient IDA.

The cooling_cpufreq_lock was being used to protect cpufreq_dev_count as
well as the IDR.  Rather than keep the mutex to protect a single integer,
I expanded the scope of cooling_list_lock to also cover cpufreq_dev_count.
We could also convert cpufreq_dev_count into an atomic.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>