Fix compilation warning

Fix warning in entropy.c caused by injecting seed read & write callbacks

Author: alzix

features/mbedtls/platform/TARGET_PSA/COMPONENT_PSA_SRV_IMPL/inc/default_random_seed.h

@@ -3,6 +3,8 @@
 #ifndef DEFAULT_RANDOM_SEED_H
 #define DEFAULT_RANDOM_SEED_H
 
+#include <stddef.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif

features/mbedtls/platform/inc/platform_mbed.h

@@ -17,6 +17,10 @@
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
+#if defined(TARGET_PSA)
+#include "default_random_seed.h"
+#endif
+
 #if DEVICE_TRNG
 #define MBEDTLS_ENTROPY_HARDWARE_ALT
 #endif