config: improve stale ThinkPad keyboard situation

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