AP_InertialSensor: use internal drivers for PHMINI

this gets us fast sampling

libraries/AP_InertialSensor/AP_InertialSensor.cpp

@@ -688,6 +688,10 @@ AP_InertialSensor::detect_backends(void)
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_TEST_V4) {
         _add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_ICM20608_NAME), ROTATION_ROLL_180_YAW_90));
         _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_ROLL_180_YAW_90));
+    } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PHMINI) {
+        // PHMINI uses ICM20608 on the ACCEL_MAG device and a MPU9250 on the old MPU6000 CS line
+        _add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_ICM20608_AM_NAME), ROTATION_ROLL_180));
+        _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_ROLL_180));
     }
     // also add any PX4 backends (eg. canbus sensors)
     _add_backend(AP_InertialSensor_PX4::detect(*this));