After recent changes, thermal_zone_get_trip() cannot fail, as invoked
from thermal_zone_device_register_with_trips(), so the only role of
the trips_disabled bitmask is struct thermal_zone_device is to make
handle_thermal_trip() skip trip points whose temperature was initially
zero.  However, since the unit of temperature in the thermal core is
millicelsius, zero may very well be a valid temperature value at least
in some usage scenarios and the trip temperature may as well change
later.  Thus there is no reason to permanently disable trip points
with initial temperature equal to zero.

Accordingly, drop the trips_disabled bitmask along with the code
related to it.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>