move util methods to dbusutil header

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ie57b106c2d4f28220986d0ab0324459dec2d6085
diff --git a/dbus/dbusutil.hpp b/dbus/dbusutil.hpp
index 54126cf..8bd2824 100644
--- a/dbus/dbusutil.hpp
+++ b/dbus/dbusutil.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <stdexcept>
+#include <string>
 
 namespace pid_control
 {
@@ -22,4 +23,9 @@
     }
 };
 
+std::string getSensorPath(const std::string& type, const std::string& id);
+std::string getMatch(const std::string& type, const std::string& id);
+void scaleSensorReading(const double min, const double max, double& value);
+bool validType(const std::string& type);
+
 } // namespace pid_control