fdtdir /dtb-3.15.0-0.rc3.git4.1.fc21.armv7hl/
Note that this says rc3, instead of rc4. After changing this to rc4, the system would
boot again. (And asked me fort the initial setup, including new root password to my surprise)
So I think there is an issue with the extlinux.conf file in the latest packages.
Regards,
Rob Lievaart.