arm: omap2: am43xx: Enable CONFIG_DM_USB

Enable CONFIG_DM_USB to remove compile warning for
am43xx based targets:

===================== WARNING ======================
This board does not use CONFIG_DM_USB. Please update
the board to use CONFIG_DM_USB before the v2019.07 release.
Failure to update by the deadline may result in board removal.
See doc/driver-model/MIGRATION.txt for more info.
====================================================

Signed-off-by: Suniel Mahesh <sunil.m@techveda.org>
diff --git a/configs/am43xx_evm_qspiboot_defconfig b/configs/am43xx_evm_qspiboot_defconfig
index 06268ba..b1bf670 100644
--- a/configs/am43xx_evm_qspiboot_defconfig
+++ b/configs/am43xx_evm_qspiboot_defconfig
@@ -50,6 +50,7 @@
 CONFIG_SPI=y
 CONFIG_TI_QSPI=y
 CONFIG_USB=y
+CONFIG_DM_USB=y
 CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_DWC3=y
 CONFIG_USB_DWC3=y