ARM: imx: Enable SDP download in SPL on DH i.MX6 DHSOM

Enable SDP protocol support in SPL for DH i.MX6 DHSOM, now that those
components fit into the SPL due to LTO.

To start U-Boot via SDP upload on i.MX6 DHSOM based board, proceed as follows:
- Compile imx_usb [1] .
- Power off the i.MX6 DHSOM based board.
- Connect both USB-serial console and USB-OTG miniB ports to host PC.
- Switch board to USB boot mode.
- Power on the board.
- Verify using '$ dmesg' that a new device has been detected as follows:
    New USB device found, idVendor=15a2, idProduct=0054, bcdDevice= 0.01
    New USB device strings: Mfr=1, Product=2, SerialNumber=0
    Product: SE Blank ARIK
    Manufacturer: Freescale SemiConductor Inc

- Upload U-Boot SPL:
$ imx_usb u-boot-with-spl.imx

- Wait for SPL to come up, the following print ought to be the last on
  UART console:
SDP: handle requests...

- Upload U-Boot proper:
$ imx_usb u-boot.img

[1] https://github.com/boundarydevices/imx_usb_loader.git

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/configs/dh_imx6_defconfig b/configs/dh_imx6_defconfig
index 3487cc2..29b0782 100644
--- a/configs/dh_imx6_defconfig
+++ b/configs/dh_imx6_defconfig
@@ -39,6 +39,10 @@
 CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x11400
+CONFIG_SPL_USB_HOST=y
+CONFIG_SPL_USB_GADGET=y
+CONFIG_SPL_USB_SDP_SUPPORT=y
+CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_MAXARGS=32
 CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_MEMTEST=y
@@ -113,6 +117,7 @@
 CONFIG_USB_GADGET_VENDOR_NUM=0x0525
 CONFIG_USB_GADGET_PRODUCT_NUM=0xa4a5
 CONFIG_CI_UDC=y
+CONFIG_SDP_LOADADDR=0x17ffffc0
 CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_WATCHDOG_TIMEOUT_MSECS=60000
 CONFIG_IMX_WATCHDOG=y