LEUART/DMA in Energy mode2 output example.

This example project reads and sends the data back to terminal using LEUART
while staying in EM2.

It uses the EFM32 CMSIS and emlib, to demonstrate the
use of LEUART communication using DMA under the EM2 on the 
EFM32WG_DK3850 development kit.

The LEUART is configured to be used with DMA under EM2.
The terminal configuration is 9600-8-N-1.
The DMA is configured to handle read and write data bytes from LEUART under EM2.

Testing:
1. Use the LEUART serial port header to connect the LEUART to your PC.
2. Configure terminal to 9600-8-N-1.
3. Enter characters from your keyboard and see if you receive the echo on the terminal.
4. Check the average current consumption is equal to EM2 on Energy Profiler.

Board:  Silicon Labs EFM32WG_DK3850 Development Kit
Device: EFM32WG990F256
