spl: Add option to enable SPL Legacy image support

Add a Kconfig option that enables Legacy image support, this allows
boards to explicitly disable this, for instance when needed for
security reasons.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Move to common/spl/Kconfig]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 6abbccd..d974271 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -23,6 +23,14 @@
 	  is y. If this is not set, SPL will move on to other available
 	  boot media to find a suitable image.
 
+config SPL_LEGACY_IMAGE_SUPPORT
+	bool "Support SPL loading and booting of Legacy images"
+	default y
+	help
+	  SPL will support loading and booting Legacy images when this option
+	  is y. If this is not set, SPL will move on to other available
+	  boot media to find a suitable image.
+
 config SPL_SYS_MALLOC_SIMPLE
 	bool
 	depends on SPL