AP_HAL: added hal.util->set_imu_target_temp() API

libraries/AP_HAL/AP_HAL_Boards.h

@@ -158,6 +158,8 @@
 #else
 #define CONFIG_HAL_BOARD_SUBTYPE HAL_BOARD_SUBTYPE_PX4_V2
 #define HAL_STORAGE_SIZE            16384
+#define HAL_HAVE_IMU_HEATER         1 // for Pixhawk2
+#define HAL_IMU_TEMP_DEFAULT       -1 // disabled
 #endif
 #define HAL_GPIO_A_LED_PIN        27
 #define HAL_GPIO_B_LED_PIN        26
@@ -206,6 +208,8 @@
 #define HAL_BARO_DEFAULT HAL_BARO_MS5607_I2C
 #define HAL_BARO_MS5607_I2C_BUS 1
 #define HAL_BARO_MS5607_I2C_ADDR 0x77
+#define HAL_HAVE_IMU_HEATER 1
+#define HAL_IMU_TEMP_DEFAULT 55
 #define HAL_UTILS_HEAT HAL_LINUX_HEAT_PWM
 #define HAL_LINUX_HEAT_PWM_NUM  6
 #define HAL_LINUX_HEAT_KP 20000
@@ -499,3 +503,7 @@
 #ifndef HAL_PARAM_DEFAULTS_PATH
 #define HAL_PARAM_DEFAULTS_PATH NULL
 #endif
+
+#ifndef HAL_HAVE_IMU_HEATER
+#define HAL_HAVE_IMU_HEATER 0
+#endif

libraries/AP_HAL/Util.h

@@ -89,8 +89,11 @@ public:
     virtual AP_HAL::Stream *get_shell_stream() { return NULL; }
 
     /* Support for an imu heating system */
-    virtual void set_imu_temp(float current) {}
+    virtual void set_imu_temp(float current) {};
 
+    /* Support for an imu heating system */
+    virtual void set_imu_target_temp(int8_t *target) {};
+    
     /*
       performance counter calls - wrapper around original PX4 interface
      */