Add PSA crypto module

New module psa_crypto.c (MBEDTLS_PSA_CRYPTO_C):
Platform Security Architecture compatibility layer on top of
libmedcrypto.

Implement psa_crypto_init function which sets up a RNG.

Add a mbedtls_psa_crypto_free function which deinitializes the
library.

Define a first batch of error codes.
diff --git a/library/version_features.c b/library/version_features.c
index 777b603..b77bf26 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -678,6 +678,9 @@
 #if defined(MBEDTLS_POLY1305_C)
     "MBEDTLS_POLY1305_C",
 #endif /* MBEDTLS_POLY1305_C */
+#if defined(MBEDTLS_PSA_CRYPTO_C)
+    "MBEDTLS_PSA_CRYPTO_C",
+#endif /* MBEDTLS_PSA_CRYPTO_C */
 #if defined(MBEDTLS_RIPEMD160_C)
     "MBEDTLS_RIPEMD160_C",
 #endif /* MBEDTLS_RIPEMD160_C */