Change the memory management on FreeRTOS to heap_4

We're migrating from heap_2 to heap_4 to avoid memory fragmentation,
since we're making several alls to pvMalloc() with different sizes.

FreeRTOS/heap_2.c

@@ -76,6 +76,7 @@
  * See heap_1.c, heap_3.c and heap_4.c for alternative implementations, and the
  * memory management pages of http://www.FreeRTOS.org for more information.
  */
+
 #include <stdlib.h>
 
 /* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
@@ -88,6 +89,8 @@ task.h is included from an application file. */
 
 #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE
 
+#ifdef USE_HEAP_2
+
 /* A few bytes might be lost to byte aligning the heap start address. */
 #define configADJUSTED_HEAP_SIZE	( configTOTAL_HEAP_SIZE - portBYTE_ALIGNMENT )
 
@@ -301,3 +304,4 @@ uint8_t *pucAlignedHeap;
 	pxFirstFreeBlock->pxNextFreeBlock = &xEnd;
 }
 /*-----------------------------------------------------------*/
+#endif