AP_HAL: added missing CONFIG_HAL_BOARD_SUBTYPE #define for HAL_BOARD_VRBRAIN
AP_HAL: VRBRAIN boards, added terrain folder and corrected EEPROM size.
VRBRAIN: modified target clean
AP_relay: added default relay pin for VRBRAIN
AP_HAL_VRBRAIN: added management for external relay 1 and 2
VRBRAIN: added startup of internal mag's driver for VR Brain Standard 5