Add debug mode

Description:
    1. Could enable debug mode by adding file: /etc/thermal.d/debugging.
        $ mkdir /etc/thermal.d
        $ touch /etc/thermal.d/debugging
        $ systemctl restart phosphor-pid-control

    2. Could record fans output PWM, chosen temperature, PID/stepwise output PWM in debug mode.

Design:
    1. Create debugging file and restart service to enable debug mode.

    2. Check if debug mode is enabled to output fans output PWM, chosen temperature,
       PID/stepwise output PWM, and so on.

Test Case:
    1. Enable debug mode and check logs: pass

Change-Id: I8527ebcb81e723298ba7e786b4501f986ebd439e
Signed-off-by: Bonnie Lo <Bonnie_Lo@wiwynn.com>
diff --git a/pid/thermalcontroller.cpp b/pid/thermalcontroller.cpp
index 71374a1..8778719 100644
--- a/pid/thermalcontroller.cpp
+++ b/pid/thermalcontroller.cpp
@@ -17,6 +17,7 @@
 #include "thermalcontroller.hpp"
 
 #include "errors/exception.hpp"
+#include "tuning.hpp"
 #include "util.hpp"
 #include "zone.hpp"
 
@@ -98,6 +99,12 @@
         value = 0;
     }
 
+    if (debugEnabled)
+    {
+        std::cerr << getID() << " choose the temperature value: " << value
+                  << "\n";
+    }
+
     return value;
 }
 
@@ -125,6 +132,11 @@
 {
     _owner->addSetPoint(value, _id);
 
+    if (debugEnabled)
+    {
+        std::cerr << getID() << " pid output pwm: " << value << "\n";
+    }
+
     return;
 }