AOSP kernel build is missing device tree blob

After building latest AOSP from source lunch db845c-userdebug and flashing it to the board (db845c), I tried to replace the kernel too. However the device tree seems to be missing somehow so it never gets started, Is there some recent instruction how to get the dtb into the vender boot image?

BootLinux: failed to get dtbo image
DTB offset is incorrect, kernel image does not have appended DTB

Root cause of the problem was using this instruction:
https://source.android.com/setup/build/building-kernels (incorrect)

instead of this:
https://source.android.com/setup/build/devices#845cdragonboard (correct)

These lines built a working kernel for me:

mkdir repo-common
cd repo-common
repo init -u https://android.googlesource.com/kernel/manifest -b common-android-mainline
repo sync -j8 -c
rm -rf out
BUILD_CONFIG=common/build.config.db845c ./build/build.sh