boards: arm: Add support for Silabs EFM32WG-STK3800

The EFM32 Wonder Gecko Starter Kit contains sensors and
peripherals demonstarting the usage of the EFM32WG MCU
family. This patch add basic support for this board.

Signed-off-by: Christian Taedcke <hacking@taedcke.com>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
13 files changed