pico-imx7d: Add Falcon mode support

Falcon mode boots the kernel directly from SPL, without loading
the full U-Boot.

As pico-imx7d does not have a GPIO for selecting Falcon versus
normal mode, enter in Falcon mode when the customer selects
the CONFIG_SPL_OS_BOOT option in menuconfig.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

board/technexion/pico-imx7d/spl.c

@@ -13,6 +13,14 @@
 #include <spl.h>
 
 #if defined(CONFIG_SPL_BUILD)
+
+#ifdef CONFIG_SPL_OS_BOOT
+int spl_start_uboot(void)
+{
+	return 0;
+}
+#endif
+
 static struct ddrc ddrc_regs_val = {
 	.mstr		= 0x01040001,
 	.rfshtmg	= 0x00400046,