drivers: thermal: Add support to disable a thermal zone by default

Certain thermal zone rules has to be enabled based on usecases. These
usecases will demand a certain thermal zone be disabled by default and
those rules will be enabled by user space daemons.

Add support for a new device tree property, which will keep the thermal
zone disabled by default.

Change-Id: I59b542aa551ad4d414e0c87c4a58ec0aa1c9901f
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>