thermal: tegra: Introduce struct trip_temps for critical and hot trips

Introduce a helper structure, struct trip_temps, for storing the
temperatures of the critical and hot trip points.

This helps to make the code in tegra_tsensor_get_hw_channel_trips()
somewhat cleaner and will be useful subsequently in eliminating
iteration over trip indices from the driver.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/9333090.CDJkKcVGEf@rjwysocki.net