boot: Call flush() before booting

In a lot of cases kernel resets UART HW. To ensure that U-Boot messages
printed before booting the kernel are not lost, call new U-Boot console
flush() function.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/bootm_os.c b/boot/bootm_os.c
index f31820c..079224c 100644
--- a/boot/bootm_os.c
+++ b/boot/bootm_os.c
@@ -303,6 +303,7 @@
 #else
 	printf("## Starting vxWorks at 0x%08lx\n", (ulong)images->ep);
 #endif
+	flush();
 
 	boot_jump_vxworks(images);