We have no experience with enabling spread spectrum.
With the 2015.04-toradex U-Boot we use the IVT/DCD table approach. So you would have to convert that to a plugin approach as in the nxp community article.
The following with its includes setup the DCD table for Apalis iMX6:
We are currently transitioning to a 2016.11 based U-Boot and we transition to use a SPL which sets up the DDR RAM.
I guess that the spread spectrum feature could be initialized from the SPL before setting up DDR.
E.g. before the call to spl_dram_init(); (or ccgr_init() ?).
To build U-Boot with SPL
$ make apalis_imx6_defconfig
$ make u-boot-with-spl.imx
And deploy the resulting u-boot-with-spl.imx as you would have with u-boot.imx before.