common: image_sign_info helper functions in SPL

Do not build image_sign_info helper functions in SPL if not needed.

Fixes: b983cc2da0ba ("lib: rsa: decouple rsa from FIT image verification")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/common/Kconfig b/common/Kconfig
index ee4f748..30cba15 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -1060,3 +1060,14 @@
 	select SHA256
 	help
 	  Enable image_sign_info helper functions.
+
+if IMAGE_SIGN_INFO
+
+config SPL_IMAGE_SIGN_INFO
+	bool
+	select SHA1
+	select SHA256
+	help
+	  Enable image_sign_info helper functions in SPL.
+
+endif