sensors: split building from manager object

To increase testability, split out the building of sensors
from the sensor manager.  And this further splits out building
from a configuration file.

Tested: Verified code continued to build and link.
Tested: Ran on quanta-q71l board and it behaved as expected.

Change-Id: Ib63a11e1107b1864c3c370bba2bd9ef2effa42f3
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index ea2a963..8740fb4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -46,6 +46,8 @@
 	sysfs/util.cpp \
 	sensors/pluggable.cpp \
 	sensors/host.cpp \
+	sensors/builder.cpp \
+	sensors/builderconfig.cpp \
 	sensors/manager.cpp \
 	pid/ec/pid.cpp \
 	pid/controller.cpp \