For anyone who is in interest, here are the complete Marlin 2.0 (Dated 25.05.2019) firmware for the Hardware combination:

1. Ender 3
2. BigTreeTech SKR 1.3
3. TMC2208 UART Mode

Flashing the 32Bit ARM SKR Board is very simple, just drop the “firmware.bin” binary on a Micro SD card, push it in the slot on the mainboard, start your printer, wait and done.

Firmware Binary (SHA1 e41791671301d02631e64aac8b350566aa3f4cbb)
Complete Firmware Source

Have fun!