Enhance fit_check_sign to check all images

At present this tool only checks the configuration signing. Have it also
look at each of the images in the configuration and confirm that they
verify.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de> (v1)

include/bootm.h

@@ -41,6 +41,8 @@ void lynxkdi_boot(image_header_t *hdr);
 
 boot_os_fn *bootm_os_get_boot_func(int os);
 
+int bootm_host_load_images(const void *fit, int cfg_noffset);
+
 int boot_selected_os(int argc, char * const argv[], int state,
 		     bootm_headers_t *images, boot_os_fn *boot_fn);