imx: mx6sllevk: add usb support

Add usb support for mx6sllevk board.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/configs/mx6sllevk_plugin_defconfig b/configs/mx6sllevk_plugin_defconfig
index e6be979..63d5bbc 100644
--- a/configs/mx6sllevk_plugin_defconfig
+++ b/configs/mx6sllevk_plugin_defconfig
@@ -11,6 +11,7 @@
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_I2C=y
+CONFIG_CMD_USB=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_PING=y
@@ -35,3 +36,7 @@
 CONFIG_DM_REGULATOR_PFUZE100=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
+CONFIG_USB=y
+CONFIG_DM_USB=y
+CONFIG_USB_EHCI_HCD=y
+CONFIG_USB_STORAGE=y