mx6sabreauto: Add Falcon mode support

Add support for Falcon mode and explain in the README the steps to
boot the kernel directly without loading the full U-Boot.

Signed-off-by: Diego Dorta <diego.dorta@nxp.com>
Acked-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/board/freescale/mx6sabreauto/mx6sabreauto.c b/board/freescale/mx6sabreauto/mx6sabreauto.c
index bfd5ffa..a8fe251 100644
--- a/board/freescale/mx6sabreauto/mx6sabreauto.c
+++ b/board/freescale/mx6sabreauto/mx6sabreauto.c
@@ -745,6 +745,13 @@
 #include <spl.h>
 #include <libfdt.h>
 
+#ifdef CONFIG_SPL_OS_BOOT
+int spl_start_uboot(void)
+{
+	return 0;
+}
+#endif
+
 static void ccgr_init(void)
 {
 	struct mxc_ccm_reg *ccm = (struct mxc_ccm_reg *)CCM_BASE_ADDR;