Add stepwise controller

This adds the ability to use stepwise curves alongside
pid control. This creates a base controller class that
pidcontroller and stepwise controller inherit from.

Note: Hysteresis to come in follow-on patch

Tested-by:
Created a stepwise controller and noticed that when it
crossed a threshold that it contributed to the pwm setting.

Change-Id: I6cf842f80eaccafc905d620970afe91e2092d568
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/Makefile.am b/Makefile.am
index a46ffd0..23f39bb 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -54,9 +54,11 @@
 	sensors/builderconfig.cpp \
 	sensors/manager.cpp \
 	pid/ec/pid.cpp \
-	pid/controller.cpp \
+	pid/ec/stepwise.cpp \
 	pid/fancontroller.cpp \
 	pid/thermalcontroller.cpp \
+	pid/pidcontroller.cpp \
+	pid/stepwisecontroller.cpp \
 	pid/builder.cpp \
 	pid/builderconfig.cpp \
 	pid/zone.cpp \