board: sl28: enable USB periheral support and gadgets

Enable support to update the board via the DFU protocol and make it
possible to export the block devices via USB mass storage protocol.

This will not work out of the box, yet. You have to change the dr_mode
of the usb0 controller to peripheral manually to make it work. True, OTG
support will hopefully coming soon.
Signed-off-by: NMichael Walle <michael@walle.cc>
Reviewed-by: NPriyanka Jain <priyanka.jain@nxp.com>

configs/kontron_sl28_defconfig

@@ -39,12 +39,14 @@ CONFIG_SYS_SPI_U_BOOT_OFFS=0x230000
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_NVEDIT_EFI=y
+CONFIG_CMD_DFU=y
 CONFIG_CMD_DM=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_PCI=y
 CONFIG_CMD_USB=y
+CONFIG_CMD_USB_MASS_STORAGE=y
 CONFIG_CMD_CACHE=y
 CONFIG_CMD_EFIDEBUG=y
 CONFIG_CMD_RNG=y
@@ -92,10 +94,13 @@ CONFIG_FSL_DSPI=y
 CONFIG_NXP_FSPI=y
 CONFIG_USB=y
 # CONFIG_SPL_DM_USB is not set
+CONFIG_DM_USB_GADGET=y
 CONFIG_USB_XHCI_HCD=y
 # CONFIG_USB_XHCI_FSL is not set
 CONFIG_USB_DWC3=y
 CONFIG_USB_DWC3_LAYERSCAPE=y
+CONFIG_USB_GADGET=y
+CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_OF_LIBFDT_ASSUME_MASK=0x0
 CONFIG_OF_LIBFDT_OVERLAY=y
 CONFIG_EFI_SET_TIME=y