linux-aspeed: Add loop device support in defconfig

CONFIG_BLK_DEV_LOOP is needed for legacy code update, and it is removed
accidently in linux 4.17 kernel's change.

Tested: Successfully run legacy code update on Romulus.

Change-Id: Ifb5c3829dd0bbd83813f696dc88b092128e65026
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/meta-openbmc-bsp/meta-aspeed/recipes-kernel/linux/linux-aspeed/ast2400/defconfig b/meta-openbmc-bsp/meta-aspeed/recipes-kernel/linux/linux-aspeed/ast2400/defconfig
index 6b3f897..d24fe84 100644
--- a/meta-openbmc-bsp/meta-aspeed/recipes-kernel/linux/linux-aspeed/ast2400/defconfig
+++ b/meta-openbmc-bsp/meta-aspeed/recipes-kernel/linux/linux-aspeed/ast2400/defconfig
@@ -79,6 +79,7 @@
 CONFIG_MTD_UBI=y
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_MTD_UBI_BLOCK=y
+CONFIG_BLK_DEV_LOOP=y
 CONFIG_BLK_DEV_RAM=y
 CONFIG_ASPEED_LPC_CTRL=y
 CONFIG_ASPEED_LPC_SNOOP=y