psa: Add PSA Crypto configuration

Add an option that can enable the exposure of PSA Crypto APIs from
libmbedcrypto.

include/mbedtls/config.h

@@ -2590,6 +2590,25 @@
  */
 #define MBEDTLS_POLY1305_C
 
+/**
+ * \def MBEDTLS_PSA_CRYPTO_C
+ *
+ * Enable the Platform Security Architecture cryptography API.
+ *
+ * \note This option only has an effect when the build option
+ * USE_CRYPTO_SUBMODULE is also in use.
+ *
+ * \warning This feature is experimental and available on an opt-in basis only.
+ * PSA APIs are subject to change at any time. The implementation comes with
+ * less assurance and support than the rest of Mbed TLS.
+ *
+ * Module:  crypto/library/psa_crypto.c
+ *
+ * Requires: MBEDTLS_CTR_DRBG_C, MBEDTLS_ENTROPY_C
+ *
+ */
+//#define MBEDTLS_PSA_CRYPTO_C
+
 /**
  * \def MBEDTLS_RIPEMD160_C
  *