Last weekend I took some time to bring up a DT-enabled 3.12 kernel on my
PandaBoard starting from your Debian netinstall image. I documented my
efforts here. During the course of this effort I found that u-boot
will fail to place the initramfs image in accessible address space if a
DeviceTree is provided. In this case the boot would fail while unpacking
the initramfs with a very non-obvious error. To avoid this I had to
constrain u-boot by adding,
to uEnv.txt (as documented here).
This took quite some time to figure out so I thought I might let you
know. You might consider doing something along these lines in the
default uEnv configuration.