sim: Thermal support for Linux

This patch enables Linux to read the temperature using hwmon infrastructure.
In order to use this in your gem5 you need to compile the kernel using the
following configs:

CONFIG_HWMON=y
CONFIG_SENSORS_VEXPRESS=y

And a proper dts file (containing an entry such as):

dcc {
 compatible = "arm,vexpress,config-bus";
 arm,vexpress,config-bridge = <&v2m_sysreg>;

  temp@0 {
   compatible = "arm,vexpress-temp";
   arm,vexpress-sysreg,func = <4 0>;
   label = "DCC";
  };
};

src/dev/arm/rv_ctrl.hh

@@ -44,6 +44,7 @@
 #include "dev/io_device.hh"
 #include "params/RealViewCtrl.hh"
 #include "params/RealViewOsc.hh"
+#include "params/RealViewTemperatureSensor.hh"
 
 /** @file
  * This implements the simple real view registers on a PBXA9
@@ -219,5 +220,32 @@ class RealViewOsc
     void clockPeriod(Tick clock_period);
 };
 
+/**
+ * This device implements the temperature sensor used in the
+ * RealView/Versatile Express platform.
+ *
+ * See ARM DUI 0447J (ARM  Motherboard Express uATX -- V2M-P1).
+ */
+class RealViewTemperatureSensor
+    : public SimObject, RealViewCtrl::Device
+{
+  public:
+    RealViewTemperatureSensor(RealViewTemperatureSensorParams *p)
+    : SimObject(p),
+      RealViewCtrl::Device(*p->parent, RealViewCtrl::FUNC_TEMP,
+                           p->site, p->position, p->dcc, p->device),
+      system(p->system)
+    {}
+    virtual ~RealViewTemperatureSensor() {};
+
+  public: // RealViewCtrl::Device interface
+    uint32_t read() const override;
+    void write(uint32_t temp) override {}
+
+  protected:
+    /** The system this RV device belongs to */
+    System * system;
+};
+
 
 #endif // __DEV_ARM_RV_HH__