vendor.sh: Confirm if need_files=n

Users running setmac on an X200 tarball for example, will
now see it being modified, if they didn't specify
setmac keep, so they might think vendor files are being
inserted, which they are not.

Therefore, a confirmation is provided at the end of the output.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/vendor.sh

@@ -410,6 +410,10 @@ vendor_inject()
 		    && printf "DO NOT flash images from '%s'\n" \
 		    "$archive" 1>&2
 
+	[ "$need_files" = "n" ] && printf \
+	    "Board '%s' doesn't use vendorfiles, so none were inserted.\n" \
+	    "$board"
+
 	#
 	# catch-all error handler, for libreboot release opsec:
 	#