Possibly this applies to other smartcard readers, too (will try later using anotherone).
Here is a picture of where the system gets stuck:
The ReinerSCT which disturbs the coreboot start process is the following:
idVendor=0c4b, idProduct=0501, bcdDevice= 0.01
Product: cyberJack RFID komfort
Manufacturer: REINER SCT
I also tried a Kobil which didn’t accect the start process at all:
idVendor=0d46, idProduct=3014, bcdDevice= 0.25
Product: Smart Token
Manufacturer: KOBIL Systems