control: Log target changes in flight recorder

With this there will be a history of how the fans were changing over
time.  There's a 20 entry limit in the flight recorder so it will always
just show the 20 latest target changes.

Example:
zone-set-target0: Set target 10500 (from 11300)"

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I93b55eea5ef288bc069eb6c29a15770165067848
1 file changed