thermal: core: move passive attr to tz->device.groups

This patch moves the passive attribute to tz->device.groups. Moving the
passive attribute also requires a .is_visible() callback implementation
for its attribute group.

The logic behind the visibility of passive attribute is kept the same.
We only expose the passive attribute if the thermal driver has exposed
at least one passive trip point.

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>