Find hwmon instances from OF device paths

Provide a method that scans the hwmon subtree for a matching
open firmware device path.

Change-Id: Ic71dea90113c6894d9d2b61e03bd02f6b550e1e6
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/Makefile.am b/Makefile.am
index 6325121..ab4d373 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -11,6 +11,7 @@
 	directory.cpp \
 	sensorset.cpp \
 	mainloop.cpp \
+	sysfs.cpp \
 	xyz.openbmc_project.Sensor.Value.cpp
 
 SUBDIRS = . test