AP_Compass: add and use AP_COMPASS_RM3100_ENABLED

libraries/AP_Compass/AP_Compass.cpp

@@ -1228,7 +1228,7 @@ void Compass::_probe_external_i2c_compasses(void)
 #endif
 #endif  // AP_COMPASS_MMC3416_ENABLED
 
-#if AP_COMPASS_I2C_BACKEND_DEFAULT_ENABLED || defined(HAL_USE_I2C_MAG_RM3100)
+#if AP_COMPASS_RM3100_ENABLED
 #ifdef HAL_COMPASS_RM3100_I2C_ADDR
     const uint8_t rm3100_addresses[] = { HAL_COMPASS_RM3100_I2C_ADDR };
 #else
@@ -1252,7 +1252,7 @@ void Compass::_probe_external_i2c_compasses(void)
         }
     }
 #endif
-#endif
+#endif  // AP_COMPASS_RM3100_ENABLED
 
 #if AP_COMPASS_BMM150_DETECT_BACKENDS_ENABLED
     // BMM150 on I2C

libraries/AP_Compass/AP_Compass.h

@@ -459,7 +459,9 @@ private:
 #if AP_COMPASS_IST8308_ENABLED
         DRIVER_IST8308  =15,
 #endif
+#if AP_COMPASS_RM3100_ENABLED
 		DRIVER_RM3100   =16,
+#endif
 #if AP_COMPASS_MSP_ENABLED
         DRIVER_MSP      =17,
 #endif

libraries/AP_Compass/AP_Compass_RM3100.cpp

@@ -19,6 +19,8 @@
  */
 #include "AP_Compass_RM3100.h"
 
+#if AP_COMPASS_RM3100_ENABLED
+
 #include <AP_HAL/AP_HAL.h>
 #include <utility>
 #include <AP_Math/AP_Math.h>
@@ -242,3 +244,5 @@ void AP_Compass_RM3100::read()
 {
 	drain_accumulated_samples(compass_instance);
 }
+
+#endif  // AP_COMPASS_RM3100_ENABLED

libraries/AP_Compass/AP_Compass_RM3100.h

@@ -14,6 +14,10 @@
  */
 #pragma once
 
+#include "AP_Compass_config.h"
+
+#if AP_COMPASS_RM3100_ENABLED
+
 #include <AP_Common/AP_Common.h>
 #include <AP_HAL/AP_HAL.h>
 #include <AP_HAL/Device.h>
@@ -58,3 +62,5 @@ private:
     enum Rotation rotation;
     float _scaler = 1.0;
 };
+
+#endif  // AP_COMPASS_RM3100_ENABLED

libraries/AP_Compass/AP_Compass_config.h

@@ -94,3 +94,7 @@
 #ifndef AP_COMPASS_QMC5883L_ENABLED
 #define AP_COMPASS_QMC5883L_ENABLED AP_COMPASS_I2C_BACKEND_DEFAULT_ENABLED
 #endif
+
+#ifndef AP_COMPASS_RM3100_ENABLED
+#define AP_COMPASS_RM3100_ENABLED AP_COMPASS_I2C_BACKEND_DEFAULT_ENABLED
+#endif