恢复system heap，调用系统接口的时候可能需要

Signed-off-by: huhui <huhui@sharkgulf.com>

Librarys/CMSIS/GD32F3x0/Source/startup_gd32f3x0.s

@@ -48,7 +48,7 @@ __initial_sp
 ;   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
 ; </h>
 
-Heap_Size       EQU     0x00000000
+Heap_Size       EQU     0x00000400
 
                 AREA    HEAP, NOINIT, READWRITE, ALIGN=3
 __heap_base