secure_storage: re-add MbedTLS backend

Re-add the option to use the MbedTLS ITS backend on posix. This backend
is much simpler to setup than the Zephyr backends in a testing
environment. This was previously removed in:
  #82319

Signed-off-by: Jordan Yates <[email protected]>

Author: JordanYates

modules/mbedtls/configs/config-tls-generic.h

@@ -486,6 +486,11 @@
 #define MBEDTLS_PSA_CRYPTO_STORAGE_C
 #endif
 
+#if defined(CONFIG_SECURE_STORAGE_ITS_IMPLEMENTATION_MBEDTLS)
+#define MBEDTLS_PSA_ITS_FILE_C
+#define MBEDTLS_FS_IO
+#endif
+
 #endif /* CONFIG_MBEDTLS_PSA_CRYPTO_C */
 
 #if defined(CONFIG_MBEDTLS_PSA_STATIC_KEY_SLOTS)

subsys/secure_storage/Kconfig

@@ -27,6 +27,12 @@ source "subsys/logging/Kconfig.template.log_config"
 choice SECURE_STORAGE_ITS_IMPLEMENTATION
 	prompt "Internal Trusted Storage (ITS) API implementation"
 
+config SECURE_STORAGE_ITS_IMPLEMENTATION_MBEDTLS
+	bool "MbedTLS ITS implementation"
+	depends on ARCH_POSIX
+	help
+	  Use MbedTLS's implementation of the ITS API.
+
 config SECURE_STORAGE_ITS_IMPLEMENTATION_ZEPHYR
 	bool "Zephyr's ITS implementation"
 	select SECURE_STORAGE_ITS_TRANSFORM_MODULE