I ran into a problem with it saying that the register_framebuffer and unregister_framebuffer functions were undefined. The kernel also refused to load the module for obvious reasons.
After chasing my tail for hours trying to link against fbmem.o I realized that it wasn't even generating the object file. I also concluded that it probably needed to enable it in the kernel. So one last make menuconfig and enabled framebuffer support. "Kernel/Library/Defaults Selection>Customize Kernel Settings" then "Device Drivers>Graphics Support>Support for frame buffer devices"