8390: select CRC32 support

The ax88796 driver uses the CRC32 functions, so make sure that
they are actually enabled.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>