Make crypto_struct internal

Move crypto_struct.h, which doen't specify the API or ABI of the library,
to the internal include folder. These headers should not get distrubuted
with our shared library, for example, as they contain implementation
details that may change between version of the shared library.

Author: Patater

include/psa/crypto_struct.h renamed to library/include/crypto_struct.h

@@ -1,5 +1,5 @@
 /**
- * \file psa/crypto_struct.h
+ * \file crypto_struct.h
  *
  * \brief PSA cryptography module: Mbed TLS structured type implementations
  *
@@ -38,7 +38,7 @@
 /* Include the Mbed TLS configuration file, the way Mbed TLS does it
  * in each of its header files. */
 #if !defined(MBEDTLS_CONFIG_FILE)
-#include "../mbedtls/config.h"
+#include "mbedtls/config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif