I can confirm setting CONFIG_HSA_AMD=y (setting it to 'm' didn't seem to work for me) made /dev/kfd available and the OpenCL ROCm work, including making OpenCL available to Darktable. Note that I tested this on a non linux-libre kernel (what I use) which may or may not be required for OpenCL on some hardware. This is on x86-64.
Are there any objections to enabling this option in our kernel config?