MLK-19881 imx8mq_arm2: Fix SPL issue to support uuu

The codes in imx8mq ARM2 SPL still return back to ROM when booting from
usb serial download. This is old way to support mfgtool not uuu.
Update the codes to support uuu when SPL SDP is enabled.

Signed-off-by: Ye Li <ye.li@nxp.com>

board/freescale/imx8mq_arm2/spl.c

@@ -194,11 +194,16 @@ int power_init_board(void)
 
 void spl_board_init(void)
 {
+#ifndef CONFIG_SPL_USB_SDP_SUPPORT
 	/* Serial download mode */
 	if (is_usb_boot()) {
 		puts("Back to ROM, SDP\n");
 		restore_boot_params();
 	}
+#endif
+
+	init_usb_clk();
+
 	puts("Normal Boot\n");
 }