common: Kconfig.boot: add config SPL_FIT_RSASSA_PSS

The padding pss is only supported on u-boot and tools since
commit 2bbed3ff8c7f ("image: Use Kconfig to enable FIT_RSASSA_PSS on host")

This commit adds the config SPL_FIT_RSASSA_PSS to support
the padding pss in the SPL.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig.boot b/common/Kconfig.boot
index 9b84a8d..c948d58 100644
--- a/common/Kconfig.boot
+++ b/common/Kconfig.boot
@@ -175,6 +175,13 @@
 	  device memory. Assure this size does not extend past expected storage
 	  space.
 
+config SPL_FIT_RSASSA_PSS
+	bool "Support rsassa-pss signature scheme of FIT image contents in SPL"
+	depends on SPL_FIT_SIGNATURE
+	help
+	  Enable this to support the pss padding algorithm as described
+	  in the rfc8017 (https://tools.ietf.org/html/rfc8017) in SPL.
+
 config SPL_LOAD_FIT
 	bool "Enable SPL loading U-Boot as a FIT (basic fitImage features)"
 	select SPL_FIT