sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/util.hpp b/util.hpp
index 7930dba..f2ffd3f 100644
--- a/util.hpp
+++ b/util.hpp
@@ -8,6 +8,9 @@
 #include <limits>
 #include <string>
 
+namespace pid_control
+{
+
 void tryRestartControlLoops(void);
 
 /*
@@ -152,3 +155,5 @@
  * Given a path that optionally has a glob portion, fill it out.
  */
 std::string FixupPath(std::string original);
+
+} // namespace pid_control