Migrate IMAGE_FORMAT_LEGACY to Kconfig

This converts IMAGE_FORMAT_LEGACY to Kconfig

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ids8313_defconfig b/configs/ids8313_defconfig
index 0a9e91e..3df3dd6 100644
--- a/configs/ids8313_defconfig
+++ b/configs/ids8313_defconfig
@@ -4,6 +4,7 @@
 CONFIG_TARGET_IDS8313=y
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
+CONFIG_IMAGE_FORMAT_LEGACY=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_BOOTDELAY=1