dm: arm: ls1021a: Move to driver model for USB

This patch enables driver model for USB in defconfigs for LS1021A
platforms.

Signed-off-by: Alison Wang <alison.wang@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/configs/ls1021aqds_nand_defconfig b/configs/ls1021aqds_nand_defconfig
index f5bbd1d..2f349ec 100644
--- a/configs/ls1021aqds_nand_defconfig
+++ b/configs/ls1021aqds_nand_defconfig
@@ -56,6 +56,7 @@
 CONFIG_PCIE_LAYERSCAPE=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
+CONFIG_DM_USB=y
 CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_DWC3=y
 CONFIG_USB_STORAGE=y