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_fdc.c b/common/cmd_fdc.c
index 1cfb656..5766b56 100644
--- a/common/cmd_fdc.c
+++ b/common/cmd_fdc.c
@@ -635,7 +635,9 @@
 	FD_GEO_STRUCT *pFG = (FD_GEO_STRUCT *)floppy_type;
 	FDC_COMMAND_STRUCT *pCMD = &cmd;
 	unsigned long addr,imsize;
+#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
 	image_header_t *hdr;  /* used for fdc boot */
+#endif
 	unsigned char boot_drive;
 	int i,nrofblk;
 #if defined(CONFIG_FIT)
@@ -689,12 +691,14 @@
 	}
 
 	switch (genimg_get_format ((void *)addr)) {
+#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
 	case IMAGE_FORMAT_LEGACY:
 		hdr = (image_header_t *)addr;
 		image_print_contents (hdr);
 
 		imsize = image_get_image_size (hdr);
 		break;
+#endif
 #if defined(CONFIG_FIT)
 	case IMAGE_FORMAT_FIT:
 		fit_hdr = (const void *)addr;