ast2500: defconfig: Add Network Block Device

Add NBD support to the defconfig as this will be used to implement
virtual media on the BMC.

This adds about 5.4kB to the kernel image:
Before:
-rw-r--r-- 2 anoo anoo  2542904 Jan 19 14:53 fitImage--4.19.16+git0+bbc22aa295-r0-witherspoon-20190119205057.bin
After:
-rw-r--r-- 2 anoo anoo  2548304 Jan 19 14:59 fitImage--4.19.16+git0+bbc22aa295-r0-witherspoon-20190119205736.bin

(From meta-aspeed rev: 1b084277f6ffedc76fece26b38e867779b5d619e)

Change-Id: I022e5f7a1067b205c83762a0aca31d77395c6d8d
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-aspeed/recipes-kernel/linux/ast2500/defconfig b/meta-aspeed/recipes-kernel/linux/ast2500/defconfig
index 8585efb..9673241 100755
--- a/meta-aspeed/recipes-kernel/linux/ast2500/defconfig
+++ b/meta-aspeed/recipes-kernel/linux/ast2500/defconfig
@@ -86,6 +86,7 @@
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_MTD_UBI_BLOCK=y
 CONFIG_BLK_DEV_LOOP=y
+CONFIG_BLK_DEV_NBD=y
 CONFIG_ASPEED_LPC_CTRL=y
 CONFIG_ASPEED_LPC_SNOOP=y
 CONFIG_ASPEED_LPC_MBOX=y