bootm: make use of legacy image format configurable

make the use of legacy image format configurable through
the config define CONFIG_IMAGE_FORMAT_LEGACY.

When relying on signed FIT images with required signature check
the legacy image format should be disabled. Therefore introduce
this new define and enable legacy image format if CONFIG_FIT_SIGNATURE
is not set. If CONFIG_FIT_SIGNATURE is set disable per default
the legacy image format.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Lars Steubesand <lars.steubesand@philips.com>
Cc: Mike Pearce <mike@kaew.be>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Michal Simek <monstr@monstr.eu>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/common/cmd_disk.c b/common/cmd_disk.c
index 3e457f6..8a1fda9 100644
--- a/common/cmd_disk.c
+++ b/common/cmd_disk.c
@@ -17,7 +17,9 @@
 	ulong addr = CONFIG_SYS_LOAD_ADDR;
 	ulong cnt;
 	disk_partition_t info;
+#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
 	image_header_t *hdr;
+#endif
 	block_dev_desc_t *dev_desc;
 
 #if defined(CONFIG_FIT)
@@ -62,6 +64,7 @@
 	bootstage_mark(BOOTSTAGE_ID_IDE_PART_READ);
 
 	switch (genimg_get_format((void *) addr)) {
+#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
 	case IMAGE_FORMAT_LEGACY:
 		hdr = (image_header_t *) addr;
 
@@ -78,6 +81,7 @@
 
 		cnt = image_get_image_size(hdr);
 		break;
+#endif
 #if defined(CONFIG_FIT)
 	case IMAGE_FORMAT_FIT:
 		fit_hdr = (const void *) addr;