Fixed battery reading for T-echo Lite

[IoTThinks]

Hi all,
This is to fix battery reading in T-Echo Lite.

• It uses GPIO 2 to read ADC
• We need to set HIGH to BATTERY_MEASUREMENT_CONTROL to read ADC.
• However, the ADC reading is not linear.

Tested with a power meter.
It is correct most of the time same as other battery reading of other boards.