VRBRAIN: modified target clean
DataFlash: Added four more channels for logging
AP_Compass: VRBRAIN. Deal with external mag connected on internal I2C on VRBRAIN 4.5
This enables user to set the external parameter to true even if only one compass is connected
AP_HAL: added missing CONFIG_HAL_BOARD_SUBTYPE #define for HAL_BOARD_VRBRAIN