lib: rsa: decouple rsa from FIT image verification

Introduce new configuration, CONFIG_RSA_VERIFY which will decouple building
RSA functions from FIT verification and allow for adding a RSA-based
signature verification for other file formats, in particular PE file
for UEFI secure boot.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
index 2b33f32..18a075c 100644
--- a/lib/rsa/Kconfig
+++ b/lib/rsa/Kconfig
@@ -18,6 +18,16 @@
 config SPL_RSA
 	bool "Use RSA Library within SPL"
 
+config SPL_RSA_VERIFY
+	bool
+	help
+	  Add RSA signature verification support in SPL.
+
+config RSA_VERIFY
+	bool
+	help
+	  Add RSA signature verification support.
+
 config RSA_SOFTWARE_EXP
 	bool "Enable driver for RSA Modular Exponentiation in software"
 	depends on DM