thermal: core: move cooling device sysfs to thermal_sysfs.c

This is a code reorganization, simply to concentrate
the sysfs handling functions in thermal_sysfs.c.

This patch moves the cooling device handling functions.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>