Add new PID Class types "power" and "powersum"

Implements this feature:
https://github.com/openbmc/phosphor-pid-control/issues/24

In addition to the existing "temp" and "margin" classes, adding
new "power" and "powersum" Class types.

The "power" class is the same as "temp", but expects D-Bus power
sensors, instead of D-Bus temperature sensors.

The "powersum" class is the same as "power", but sums together all of
the given inputs, instead of finding the maximum.

Signed-off-by: Josh Lehan <krellan@google.com>
Change-Id: I11d8ad8385632658ed061671134be87a560cd02a
diff --git a/pid/thermalcontroller.hpp b/pid/thermalcontroller.hpp
index 6144d49..752c105 100644
--- a/pid/thermalcontroller.hpp
+++ b/pid/thermalcontroller.hpp
@@ -13,12 +13,16 @@
 /*
  * A ThermalController is a PID controller that reads a number of sensors and
  * provides the setpoints for the fans.
+ * With addition of support for power sensors, this name is misleading,
+ * as it now works for power sensors also, not just thermal sensors.
+ * If rewritten today, a better name would be "ComputationType".
  */
 
 enum class ThermalType
 {
     margin,
-    absolute
+    absolute,
+    summation
 };
 
 /**