spl: sdp: Add CONFIG_SPL_SDP_USB_DEV for USB device

Add a new configuration CONFIG_SPL_SDP_USB_DEV to specify the
usb index for spl sdp driver, so that we change use different device.
The default value is 0.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/common/spl/spl_sdp.c b/common/spl/spl_sdp.c
index a54c747..82bce0b 100644
--- a/common/spl/spl_sdp.c
+++ b/common/spl/spl_sdp.c
@@ -14,9 +14,9 @@
 			      struct spl_boot_device *bootdev)
 {
 	int ret;
-	const int controller_index = 0;
+	const int controller_index = CONFIG_SPL_SDP_USB_DEV;
 
-	board_usb_init(0, USB_INIT_DEVICE);
+	board_usb_init(controller_index, USB_INIT_DEVICE);
 
 	g_dnl_clear_detach();
 	ret = g_dnl_register("usb_dnl_sdp");