mx6sabresd: Select CONFIG_CMD_USB_MASS_STORAGE

Select CONFIG_CMD_USB_MASS_STORAGE so that the 'ums' can be used.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/configs/mx6sabresd_defconfig b/configs/mx6sabresd_defconfig
index 3e4c13c..f6a53d6 100644
--- a/configs/mx6sabresd_defconfig
+++ b/configs/mx6sabresd_defconfig
@@ -32,6 +32,7 @@
 CONFIG_CMD_SF=y
 CONFIG_CMD_USB=y
 CONFIG_CMD_USB_SDP=y
+CONFIG_CMD_USB_MASS_STORAGE=y
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y