Move pk_info structure to its own file

This is in preparation to adding support for opaque keys in the pk layer. The
header files are for use as follows:

* pk.h for users of the pk interface.
* pk_info.h for implementers of opaque key engines.
* pk_internal.h only inside libmbedcrypto to implement built-in pk types.
diff --git a/include/mbedtls/pk_internal.h b/include/mbedtls/pk_internal.h
index 4823294..06475e9 100644
--- a/include/mbedtls/pk_internal.h
+++ b/include/mbedtls/pk_internal.h
@@ -1,9 +1,9 @@
 /**
- * \file pk.h
+ * \file pk_internal.h
  *
- * \brief Public Key cryptography abstraction layer: wrapper functions
+ * \brief Public Key cryptography abstraction layer: built-in key types
  *
- *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  Copyright (C) 2006-2017, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -21,8 +21,8 @@
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
-#ifndef MBEDTLS_PK_WRAP_H
-#define MBEDTLS_PK_WRAP_H
+#ifndef MBEDTLS_PK_INTERNAL_H
+#define MBEDTLS_PK_INTERNAL_H
 
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "config.h"
@@ -32,60 +32,6 @@
 
 #include "pk.h"
 
-struct mbedtls_pk_info_t
-{
-    /** Key pair type with indication of supported algorithms */
-    mbedtls_pk_type_t type;
-
-    /** Type name */
-    const char *name;
-
-    /** Get key size in bits */
-    size_t (*get_bitlen)( const void *ctx );
-
-    /** Tell if the context implements this type (e.g. ECKEY can do ECDSA) */
-    int (*can_do)( const void * ctx, mbedtls_pk_type_t type );
-
-    /** Verify signature */
-    int (*verify_func)( void *ctx, mbedtls_md_type_t md_alg,
-                        const unsigned char *hash, size_t hash_len,
-                        const unsigned char *sig, size_t sig_len );
-
-    /** Make signature */
-    int (*sign_func)( void *ctx, mbedtls_md_type_t md_alg,
-                      const unsigned char *hash, size_t hash_len,
-                      unsigned char *sig, size_t *sig_len,
-                      int (*f_rng)(void *, unsigned char *, size_t),
-                      void *p_rng );
-
-    /** Decrypt message */
-    int (*decrypt_func)( void *ctx, const unsigned char *input, size_t ilen,
-                         unsigned char *output, size_t *olen, size_t osize,
-                         int (*f_rng)(void *, unsigned char *, size_t),
-                         void *p_rng );
-
-    /** Encrypt message */
-    int (*encrypt_func)( void *ctx, const unsigned char *input, size_t ilen,
-                         unsigned char *output, size_t *olen, size_t osize,
-                         int (*f_rng)(void *, unsigned char *, size_t),
-                         void *p_rng );
-
-    /** Check public-private key pair */
-    int (*check_pair_func)( const void *pub, const void *prv );
-
-    /** Allocate a new context */
-    void * (*ctx_alloc_func)( void );
-
-    /** Free the given context */
-    void (*ctx_free_func)( void *ctx );
-
-    /** Interface with the debug module */
-    void (*debug_func)( const void *ctx, mbedtls_pk_debug_item *items );
-
-    /** Signature size */
-    size_t (*signature_size_func)( const void *ctx );
-};
-
 #if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 /* Container for RSA-alt */
 typedef struct
@@ -114,4 +60,4 @@
 extern const mbedtls_pk_info_t mbedtls_rsa_alt_info;
 #endif
 
-#endif /* MBEDTLS_PK_WRAP_H */
+#endif /* MBEDTLS_PK_INTERNAL_H */