FreeBSD on Zynq (Cortex-A9), new Phy for cgem0?

Hello,

I’m running 14.3 on a Zynq 7020 with excellent results so far and hope to continue to use 15.+ on this platform.

The problem I now face is to support a new Phy on cgem0. Rather than modify - test - rebuild - reboot the kernel, I’d like to develop and debug cgem0+Phy as a KLD (using USB-Eth in the meantime). My platform is nearly identical to ZEDBOARD.

How do I modify the build so that cgem0 (with Phys) is built as a KLD? 
My thinking is I’d be able to modify, load, test/debug, unload the KLD faster. Am I missing anything?

Thank you.
Shiro