I didn't need to know as I used a bit of cbxbiker's script to join a zImage to a .dtb to create a uImage.
I created a .config file manually from a combination of 'make kirkwood_defconfig' and a previous non-dtb implementation (on a windows machine using WinMerge!). Cbxbikers patches for kirkwood for sheevaplug were applied manually as the patch command threw up an error. Nothing serious but it left out defining MACH_SHEEVAPLUG_DT if memory serves me correctly.
Then 'make menuconfig' to select all the options I wanted.
'make zImage'
'make dtbs'
My segment of scripts I used were as below. Hope these help.
For Guruplug:-
cat /kernel/linux-3.10/arch/arm/boot/zImage /kernel/linux-3.10/arch/arm/boot/dts/kirkwood-guruplug-server-plus.dtb > /tmp/zImage.orig
mkimage -A arm -O linux -C none -T kernel -a 0x00008000 -e 0x00008000 -n "Linux-kirkwood-guruplug-server-plus-3.10" -d /tmp/zImage.orig Linux-kirkwood-guruplug-server-plus-3.10-uImage
rm /tmp/zImage.orig
and for TP2:-
cat /kernel/linux-3.10/arch/arm/boot/zImage /kernel/linux-3.10/arch/arm/boot/dts/kirkwood-topkick.dtb > /tmp/zImage.orig
mkimage -A arm -O linux -C none -T kernel -a 0x00008000 -e 0x00008000 -n "Linux-kirkwood-topkick-3.10" -d /tmp/zImage.orig Linux-kirkwood-topkick-3.10-uImage
rm /tmp/zImage.orig
Then of course 'make modules' , 'make modules_install'.
All compiled on a esata sheevaplug. Results placed on a USB stick and inserted into each GP+ in turn and manually copied to /mnt/sda1 (/dev/sdb1 formatted as ext2) and /boot (/dev/sdb2 formatted as ext4).
BTW this posting is travelling from my PC via a GP+ set up as a router running 3.10.0 with quagga, so it works.