Please note the various meta-rockchip forks,
There is, http://git.yoctoproject.org/cgit/cgit.cgi/meta-rockchip. This is based on using mainstream components (Linux and U-boot), so no GPU support basically. I believe I used this for thud support.
There is also, https://github.com/rockchip-linux/meta-rockchip. Which is maintained by Rockchip and has GPU supported (custom Linux fork), but they have abandoned it at times, which is why I at one point created https://github.com/mirzak/meta-rockchip, and I believe I used this for the rocko integration
I would probably just focus on http://git.yoctoproject.org/cgit/cgit.cgi/meta-rockchip as this has been maintained consistently at least.