thermal: core: move thermal_zone sysfs to thermal_sysfs.c

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

Right now, moving only the sysfs entries of thermal_zone_device.

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>