drivers: of-thermal: Notify all sibling thermal zones on trip

Sibling thermal zone trips are aggregated to set the threshold on the
sensor. When the trip threshold is reached, sensor driver needs to
notify all the sibling thermal zones. But the sibling relation is not
visible to sensor driver to notify them.

Provide a new API in the thermal core, which can be used by the sensor
drivers to notify all the sibling thermal zones.

Change-Id: I8e1042cbcdc6e4ac3c252042e9525ed920f55356
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>