This yocto recipe allows you to use @thaytan's rpicamsrc element inside your custom system.
I suggest you to copy this recipe inside your custom layer, or into a brand-new one.
Suggested path should be like:
poky/meta-yourlayer/recipes-multimedia/gstreamer/gstreamer1.0-rpicamsrc.inc
poky/meta-yourlayer/recipes-multimedia/gstreamer/gstreamer1.0-rpicamsrc_0.0.1.bb
You can then test bitbake execution:
bitbake gstreamer1.0-rpicamsrc
Tested on Yocto 'Rocko', running on Raspberry Pi module B+