For those who are interested in running a more up-to-date kernel:
I took a diff of the Parallella 3.12.0 kernel and forward-ported it to 3.12.24. Surprisingly, it was mostly a clean patch, although I had to resolve some manual conflicts. The one area I'm most worried about is in drivers/dma/xilinx_dma.c; the device_prep_dma_cyclic() callback prototype has changed to include a flags parameter, and I'm not sure what should be done with that on our platform. Use of this new parameter is spotty across several other DMA drivers though (not just the Xilinx driver), so I suspect it's not that much of a problem to ignore it for now.
(I looked at the latest linux-xlnx 3.14/3.15 git tree to see what it's doing there, but the Xilinx DMA driver has been massively rearchitected and split into three pieces.)
In any event I've got the updated kernel booting, and it appears to be working reasonably well so far, given the hour or so of run-time. YMMV.
The attached patch fits right into the vanilla 3.12.24 kernel.
EDIT: really, no support for .xz? Fine, eat an extra 400K.