pid: zone split out builders

To enable unit-testing, split the builders into their own
object files.

Tested: Ran on quanta-q71l board and it behaved as expected.

Change-Id: I92168ec9ae4946d12328e9c0b94a36bb89d0f718
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 8740fb4..10cefda 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -53,6 +53,8 @@
 	pid/controller.cpp \
 	pid/fancontroller.cpp \
 	pid/thermalcontroller.cpp \
+	pid/builder.cpp \
+	pid/builderconfig.cpp \
 	pid/zone.cpp \
 	pid/util.cpp \
 	pid/pidthread.cpp \