drivers: of-thermal: Relate thermal zones using same sensor

A sensor may need to be monitored by two or more thermal governors to
deploy different mitigation strategies to control the device temperature.
To achieve this the sensors driver has to register the same sensor as
multiple thermal zones and then let the different governors monitor and
mitigate. The sensor driver should handle the aggregation of thresholds,
trip notification and synchronization between thermal zones.

Add support in of-thermal to create and handle sibling thermal zones.
Thermal zones that share the same sensor are siblings. To establish a
relationship between then the sibling zones, a sensor meta data is shared
across multiple sibling thermal zones. This meta data will aid in
traversing through all the sibling thermal zones.

Change-Id: I910c0ee15b575daff8c7636a8197da72b94ae72e
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>