rsa: add support of padding pss

We add the support of the padding pss for rsa signature.
This new padding is often recommended instead of pkcs-1.5.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Kconfig b/Kconfig
index dca9bb4..3120553 100644
--- a/Kconfig
+++ b/Kconfig
@@ -290,6 +290,14 @@
 	  device memory. Assure this size does not extend past expected storage
 	  space.
 
+config FIT_ENABLE_RSASSA_PSS_SUPPORT
+	bool "Support rsassa-pss signature scheme of FIT image contents"
+	depends on FIT_SIGNATURE
+	default n
+	help
+	  Enable this to support the pss padding algorithm as described
+	  in the rfc8017 (https://tools.ietf.org/html/rfc8017).
+
 config FIT_VERBOSE
 	bool "Show verbose messages when FIT images fail"
 	help