board: sl28: switch to dwc3 driver

Now that the DWC3 USB driver has support for the layerscape platform,
use it. This will have the benefit that peripheral mode will work.
Signed-off-by: NMichael Walle <michael@walle.cc>
Reviewed-by: NPriyanka Jain <priyanka.jain@nxp.com>

configs/kontron_sl28_defconfig

@@ -93,7 +93,9 @@ CONFIG_NXP_FSPI=y
 CONFIG_USB=y
 # CONFIG_SPL_DM_USB is not set
 CONFIG_USB_XHCI_HCD=y
-CONFIG_USB_XHCI_DWC3=y
+# CONFIG_USB_XHCI_FSL is not set
+CONFIG_USB_DWC3=y
+CONFIG_USB_DWC3_LAYERSCAPE=y
 CONFIG_OF_LIBFDT_ASSUME_MASK=0x0
 CONFIG_OF_LIBFDT_OVERLAY=y
 CONFIG_EFI_SET_TIME=y