image: Export fit_check_ramdisk()

One we split out the FIT code from image.c we will need this function.
Export it in the header.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/include/image.h b/include/image.h
index d2325dd..7149cba 100644
--- a/include/image.h
+++ b/include/image.h
@@ -633,6 +633,9 @@
 
 void fit_conf_print(const void *fit, int noffset, const char *p);
 
+int fit_check_ramdisk(const void *fit, int os_noffset,
+		uint8_t arch, int verify);
+
 #ifndef USE_HOSTCC
 static inline int fit_image_check_target_arch(const void *fdt, int node)
 {