thermal: core: Add thermal zone enable/disable notification

Now the calls to enable/disable a thermal zone are centralized in a
call to a function, we can add in these the corresponding netlink
notifications.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Link: https://lore.kernel.org/r/20200727231033.26512-1-daniel.lezcano@linaro.org