tools: Add preload_check_sign to authenticate images with a pre-load

preload_check_sign is added so that it can be used to authenticate images
signed with the pre-load signature supported by binman and U-Boot.
It could also be used to test the signature in binman tests signing
images with the pre-load.

Signed-off-by: Paul HENRYS <paul.henrys_ext@softathome.com>
diff --git a/tools/Kconfig b/tools/Kconfig
index 01ff0fc..8e272ee 100644
--- a/tools/Kconfig
+++ b/tools/Kconfig
@@ -9,6 +9,11 @@
 	  some cases the system dtc may not support all required features
 	  and the path to a different version should be given here.
 
+config TOOLS_IMAGE_PRE_LOAD
+	def_bool y
+	help
+	  Enable pre-load signature support in the tools builds.
+
 config TOOLS_CRC16
 	def_bool y
 	help