Create psa_util_internal.h

Most functions in psa_util.h are going to end up there (except those
that can be static in one file), but I wanted to have separate commits
for file creation and moving code around, so for now the new file's
pretty empty but that will change in the next few commits.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/psa_crypto_random_impl.h b/library/psa_crypto_random_impl.h
index 4197b4b..2a75a43 100644
--- a/library/psa_crypto_random_impl.h
+++ b/library/psa_crypto_random_impl.h
@@ -3,12 +3,12 @@
  * \brief PSA crypto random generator implementation abstraction.
  *
  * The definitions here need to be consistent with the declarations
- * in include/mbedtls/psa_util.h. This file contains some redundant
+ * in include/psa_util_internal.h. This file contains some redundant
  * declarations to increase the chance that a compiler will detect
  * inconsistencies if one file is changed without updating the other,
  * but not all potential inconsistencies can be enforced, so make sure
  * to check the public declarations and contracts in
- * include/mbedtls/psa_util.h if you modify this file.
+ * include/psa_util_internal.h if you modify this file.
  */
 /*
  *  Copyright The Mbed TLS Contributors
@@ -30,7 +30,7 @@
 #ifndef PSA_CRYPTO_RANDOM_IMPL_H
 #define PSA_CRYPTO_RANDOM_IMPL_H
 
-#include <mbedtls/psa_util.h>
+#include <psa_util_internal.h>
 
 #if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
 
@@ -123,7 +123,7 @@
     mbedtls_psa_drbg_context_t drbg;
 } mbedtls_psa_random_context_t;
 
-/* Defined in include/mbedtls/psa_util.h so that it's visible to
+/* Defined in include/psa_util_internal.h so that it's visible to
  * application code. The declaration here is redundant, but included
  * as a safety net to make it more likely that a future change that
  * accidentally causes the implementation to diverge from the interface
@@ -154,7 +154,7 @@
 /* psa_crypto.c sets this variable to a pointer to the DRBG state in the
  * global PSA crypto state. */
 /* The type `mbedtls_psa_drbg_context_t` is defined in
- * include/mbedtls/psa_util.h so that `mbedtls_psa_random_state` can be
+ * include/psa_util_internal.h so that `mbedtls_psa_random_state` can be
  * declared there and be visible to application code. */
 extern mbedtls_psa_drbg_context_t *const mbedtls_psa_random_state;