thermal: rcar-thermal: enable hwmon when thermal_zone_of_sensor_register is used

rcar-thermal is supporting both thermal_zone_of_sensor_register() and
thermal_zone_device_register(). But thermal_zone_of_sensor_register()
doesn't enable hwmon as default.
This patch enables it to keep compatibility

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>