OpenAmp Middleware: fix C++ specific compilation error

See STMicroelectronics/STM32CubeMP1#7
The header files including must be outside of the extern "C" { statement.
To be able to be included from C++ code

Author: ABOSTM

system/Middlewares/OpenAMP/libmetal/lib/include/metal/mutex.h

@@ -12,6 +12,12 @@
 #ifndef __METAL_MUTEX__H__
 #define __METAL_MUTEX__H__
 
+#ifdef METAL_FREERTOS
+#include <metal/system/freertos/mutex.h>
+#else
+#include <metal/system/generic/mutex.h>
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -20,12 +26,6 @@ extern "C" {
  *  @{
  */
 
-#ifdef METAL_FREERTOS
-#include <metal/system/freertos/mutex.h>
-#else
-#include <metal/system/generic/mutex.h>
-#endif
-
 /**
  * @brief	Initialize a libmetal mutex.
  * @param[in]	mutex	Mutex to initialize.

system/Middlewares/OpenAMP/virtual_driver/virt_uart.h

@@ -21,14 +21,13 @@
 #ifndef __VIRT_UART_H
 #define __VIRT_UART_H
 
+/* Includes ------------------------------------------------------------------*/
+#include "openamp.h"
 
 #ifdef __cplusplus
  extern "C" {
 #endif
 
-/* Includes ------------------------------------------------------------------*/
-#include "openamp.h"
-
 /* Exported structures --------------------------------------------------------*/
 typedef struct __VIRT_UART_HandleTypeDef
 {