i have been working on kernels for various xperia devices (around 22 devices or so ) since the Xperia X10...
FIRSTLY the kernel building instructions given by Sony in the README_Xperia are WRONG!!!
huge thanks to @Kali- to fix the dtbTools issue (Z2 needs v2 dtb)!
specific instructions on how to build kernel for Xperia Z2 can be found here:
Instructions for MSM8974AB
I have a very detailed thread with information on how to build kernels for various xperia devices:
[Tutorial] Kernel building instructions for Xperia devices
Please use this thread to post your feedback and incase you need any help with building kernels for this device!