config/aspeed: Enable NC-SI support

Aspeed BMCs are commonly used with NC-SI. A system indicates the driver
should configure the link over NC-SI using the device tree.

Add it to the defconfig so we get compile coverage of the driver, even
if the EVBs do not normally use it.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>