Temporarily disable shared Mbed TLS heap for SGM

There is a bug in the shared heap implementation for SGM. Until the bug
is solved, the default implementation is used.

Change-Id: I010911a3f00ed860f742b14daad1d99b9e7ce711
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>

plat/arm/css/sgm/sgm_plat_config.c

 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,6 +10,7 @@
 #include <platform_def.h>
 
 #include <common/debug.h>
+#include <plat/common/platform.h>
 #include <plat/arm/common/plat_arm.h>
 
 #include <sgm_plat_config.h>
@@ -74,9 +75,6 @@ css_plat_config_t *get_plat_config(void)
 #if TRUSTED_BOARD_BOOT
 int plat_get_mbedtls_heap(void **heap_addr, size_t *heap_size)
 {
-	assert(heap_addr != NULL);
-	assert(heap_size != NULL);
-
-	return arm_get_mbedtls_heap(heap_addr, heap_size);
+	return get_mbedtls_heap_helper(heap_addr, heap_size);
 }
 #endif