config: improve stale ThinkPad keyboard situation
Neither the DragonFly release nor snapshots accept the builtin keyboard
of a Lenovo T430u (and apparently a couple of others). FreeBSD as old as
8.3, however, works just fine. Turns out that the KB_CONF_FAIL_IF_NO_KBD
flag of atkbd(4) still lingers in GENERIC, SOEKRIS and X86_64_GENERIC.
Tested against regressions when hotplugging USB keyboards without a PS/2
keyboard present on an old Athlon64.
We have one panic report by sephe in the kbdsw code, which is triggered
by pressing a key on a previously unresponsive keyboard, but no further
info for debugging at this point.
Force the issue now that the release has been branched.
Backed-by: sephe, swildner