ast2500: defconfig: Add USB Mass Storage

USB Mass Storage will be used for implementing Virtual Media.

This adds about 800 bytes to the kernel image:
Before:
-rw-r--r-- 2 anoo anoo  2582512 Jan 22 09:57 fitImage--4.19.16+git0+bbc22aa295-r0-witherspoon-20190122155444.bin
After:
-rw-r--r-- 2 anoo anoo  2583344 Jan 22 10:02 fitImage--4.19.16+git0+bbc22aa295-r0-witherspoon-20190122160056.bin

Change-Id: I3ed0715cee703a1ff1389b4867057be52ee7f999
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/recipes-kernel/linux/ast2500/defconfig b/recipes-kernel/linux/ast2500/defconfig
index 2869a64..7d34e15 100755
--- a/recipes-kernel/linux/ast2500/defconfig
+++ b/recipes-kernel/linux/ast2500/defconfig
@@ -193,6 +193,7 @@
 CONFIG_USB_ASPEED_VHUB=y
 CONFIG_USB_CONFIGFS=y
 CONFIG_USB_CONFIGFS_MASS_STORAGE=y
+CONFIG_USB_MASS_STORAGE=y
 CONFIG_NEW_LEDS=y
 CONFIG_LEDS_CLASS=y
 CONFIG_LEDS_CLASS_FLASH=y