aerofc: Implement ADC

Measure the battery voltage of Aero RTF kit will be done by FPGA
and read by AeroFC using I2C bus.

The protocol is a little bit odd, it have different I2C slave
address for each "register", in future the FPGA RTL will
have a protocol more similar to other I2C sensors.

Also Aero RTF don't have a ADC line to measure current consumption.

src/drivers/boards/aerofc-v1/board_config.h

@@ -99,7 +99,7 @@
  * ADC defines just to not break sensors.cpp build, battery voltage and current
  * will be read in another way in future.
  */
-#define ADC_BATTERY_VOLTAGE_CHANNEL    0
+#define ADC_BATTERY_VOLTAGE_CHANNEL    5
 #define ADC_BATTERY_CURRENT_CHANNEL    ((uint8_t)(-1))
 
 #define DIRECT_PWM_OUTPUT_CHANNELS	1