imx6: wandboard: convert to DM_USB

Drop CONFIG_USB_MAX_CONTROLLER_COUNT and enable DM_USB
in defconfig.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
diff --git a/configs/wandboard_defconfig b/configs/wandboard_defconfig
index 11cf441..9e13d7f 100644
--- a/configs/wandboard_defconfig
+++ b/configs/wandboard_defconfig
@@ -46,6 +46,7 @@
 CONFIG_PINCTRL_IMX6=y
 CONFIG_DM_THERMAL=y
 CONFIG_USB=y
+CONFIG_DM_USB=y
 CONFIG_VIDEO=y
 CONFIG_VIDEO_IPUV3=y
 # CONFIG_VIDEO_SW_CURSOR is not set