ns8390.c can produce four different drivers (one PCI, three ISA.)  The
ISA driver requires setting a few macros; do that by setting defines
in stub files instead of using src/Config.

Currently, all the ISA drivers are broken (they were not enabled by
default), so #if 0 them out.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>