Revert "thermal-core: Add a lock to tz_notify_trip()"

This reverts commit 383ac33a.

The temperature sensor drivers registering with thermal
core framework can call the thermal_sensor_trip() API in
interrupt context. This might cause potential thermal
reset issues because the interrupt might be disabled till
this API returns.

Change-Id: I8d6dfc55386fbdea8e51e7abbb0e7632208c6c38
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>