With r181803 on 2008-08-17 23:27:27Z the first VIMAGE commit went into
HEAD. Enable VIMAGE in GENERIC kernels and some others (where GENERIC does
not exist) on HEAD.

Disable building LINT-VIMAGE with VIMAGE being default.

This should give it a lot more exposure in the run-up to 12 to help
us evaluate whether to keep it on by default or not.
We are also hoping to get better performance testing.
The feature can be disabled using nooptions.

Requested by: many
Reviewed by: kristof, emaste, hiren
X-MFC after: never
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D12639