drm-fbsd12.0-kmod built on 12.1-RELEASE causes boot hang with 12.1-STABLE kernel

[Per Hedeland]

Hi,

I'm not sure if this is old news, and I don't consider it to merit a
PR, but it seems to me (I may very well be wrong about that) that it
might indicate that the problems with the pre-built package in the
12.0-RELEASE -> 12.1-RELEASE upgrade will be repeated with
12.1-RELEASE -> 12.2-RELEASE - so just a heads-up in case it is
needed:

I was using i915kms from the port built on 12.1-RELEASE -
unfortunately I'm not 100% sure about the port version, but I believe
it was 4.16.g20191120 - certainly not newer. When trying a kernel
upgrade to 12.1-STABLE at r358121, the boot hung (with a cleared
screen...). Rebuilding the port, now at 4.16.g20200115, on the
12.1-STABLE kernel, resolved the problem.

--Per Hedeland