How to load device tree overlay on kernel 3.19+
From my experience (3.8-3.14), DTB loading is actually the jurisdiction of the boot-loader, rather than the kernel itself. I've used u-boot for this - u-boot can load the compiled device-tree file (man dtc) from an EXT2-based filesystem to a known location in RAM, which is then specified in the kernel command line.
Which boot-loader are you using?