drivers: thermal: cpu-cooling: Fix core isolation support

Cpu cooling device driver now uses the cpufreq policy data structure to
determine the related CPUs to mitigate. COre isolation support requires
the individual CPU in the related CPU to be mitigated.

Add a support to determine the CPU the cooling device refers to using
the device node. This will be used only when the device node is
specified. Otherwise the first cpu in the cpufreq policy will be used.

Change-Id: I28866a9873ed8030fc531151747592ae2fe0acdb
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>