configs: pico-imx6ul: convert DM_USB

Here is the test commands:

  => ums 0 mmc 0
  UMS: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x710000

Signed-off-by: Wig Cheng <wig.cheng@technexion.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/pico-imx6ul_defconfig b/configs/pico-imx6ul_defconfig
index 5c841c3..1db522a 100644
--- a/configs/pico-imx6ul_defconfig
+++ b/configs/pico-imx6ul_defconfig
@@ -68,6 +68,7 @@
 CONFIG_DM_REGULATOR_GPIO=y
 CONFIG_MXC_UART=y
 CONFIG_USB=y
+CONFIG_DM_USB=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_MANUFACTURER="FSL"
 CONFIG_USB_GADGET_VENDOR_NUM=0x0525