Here you go:
https://rcn-ee.net/rootfs/bb.org/testing/2022-11-30/stretch-imgtec-armhf/
It uses the 4.14.108-ti-r143 and everything is prebuilt/pre-installed with sgx enabled.
If you need any kernel changes, you can tweak the device-tree and overlays, but a kernel rebuild will require a full sgx module rebuild… So yeah, a pain…
Once booted, just run dmesg | grep pvr and you should see the SGX modules loaded and active…
dmesg | grep pvr
Regards,