Fix DES_LONG breakage

For some strange reason opensslconf.h was only defining DES_LONG
when included via des.h, but that's exceedingly fragile (as a
result of include guards the include via des.h might not actually
process the content again).

Ripped out the nesting constraint, now always define OSSL_DES_LONG
if not already defined.  Note, this could just be DES_LONG, but
trying to avoid exposing DES_LONG in places where it has never been
seen before, so it is up to des.h to actually define DES_LONG as
OSSL_DES_LONG.

Reviewed-by: Rich Salz <rsalz@openssl.org>