How to add custom device tree to build?


I would like to addd a customized device tree to my cc6ulstarter build. i’ve attempted to follow, have added the custom dtb line to the makefile but am getting stuck at adding a new custom layer to the Yocto build: On the above link under “Add new machine in custom Digi Embedded Yocto layer” it says the following: “You must copy the Linux kernel default configuration file to the meta-custom layer, as Yocto does not use the one included in the kernel tree.” but I see, there’s this file that came in when I cloned the meta-custom repo:
I then created recipes-bsp/u-boot/u-boot-dey_v2017.03.bbappend and recipes-kernel/linux/linux-dey_4.9.bbappend after which I’m not so sure how to actually invoke bitbake now to compile this, bitbake core-image-base didn’t seem to build anything even though I’ve sourced it like: $ source /usr/local/dey-3.2/ -m meta-custom -p custom
What am I missing?