Ubiquitous/RT-Thread_Fusion_XiUOS/:add xidatong-riscv64 bsp

Ubiquitous/RT-Thread_Fusion_XiUOS/aiit_board/xidatong-riscv64/base-drivers/heap.c

@@ -0,0 +1,11 @@
+#include <rtthread.h>
+#include <stdlib.h>
+
+size_t get_free_heap_size(void)
+{
+    rt_uint32_t total, used, max;
+
+    rt_memory_info(&total, &used, &max);
+
+    return total - used;
+}