These days most OpenBSD users should have the machdep.allowaperture
sysctl set to 0 (the default). Having it set to seomething else poses
security risks and can actually cause problems, in particular on
systems that have multiple GPUs where one of tha GPUs is supported by
inteldrm(4) or radeondrm(4) and the other isn't.
You'll only need to set machdep.allowaperture to a non-zero value if
inteldrm(4) or radeordrm(4) doesn't attach on your machine and you
can't use efifb(4) either.