lib: system: freertos: Add metal/errno.h to match standalone

As lib/system/generic/sys.h has metal/errno.h add this to the freertos
equivalent.

This fixes some compilation issues when linking against certain FreeRTOS port
BSPs.

Signed-off-by: Ben Levinsky <ben.levinsky@amd.com>

lib/system/freertos/sys.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2016, Xilinx Inc. and Contributors. All rights reserved.
+ * Copyright (c) 2022-2023 Advanced Micro Devices, Inc. All Rights Reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -16,6 +17,8 @@
 #ifndef __METAL_FREERTOS_SYS__H__
 #define __METAL_FREERTOS_SYS__H__
 
+#include <metal/errno.h>
+
 #include "./@PROJECT_MACHINE@/sys.h"
 
 #ifdef __cplusplus