Capactive touch example.

This example demonstrates the capacitive touch capability of the EFM32 and the
Tiny Gecko STK. This is a port of the EFM32_G8xx_STK capacitive touch demo.

It demonstrates the use of LESENSE, ACMP, VCMP, LCD, and EMU.

Board:  Silicon Labs EFM32WG_STK3800
Device: EFM32WG990F256
