test: fix inconsistent memory size

* To run more programs on debian, we use 256MB memory described in dts.
  But if the hardware still provides 128MB memory, the memory access
  will wrap around when Linux allocate a physical page excceed 128MB,
  which causes wrong memory access.

src/test/csrc/ram.cpp

 #include "common.h"
 
-#define RAMSIZE (128 * 1024 * 1024)
+#define RAMSIZE (256 * 1024 * 1024)
 #define MAINARGS_START 0x1000
 
 static uint64_t ram[RAMSIZE / sizeof(uint64_t)];

src/test/scala/top/NOOPSim.scala

@@ -35,7 +35,7 @@ class NOOPSimTop extends Module {
 
   lazy val config = NOOPConfig(FPGAPlatform = false)
   val soc = Module(new NOOPSoC()(config))
-  val mem = Module(new AXI4RAM(memByte = 128 * 1024 * 1024, useBlackBox = true))
+  val mem = Module(new AXI4RAM(memByte = 256 * 1024 * 1024, useBlackBox = true))
   // Be careful with the commit checking of emu.
   // A large delay will make emu incorrectly report getting stuck.
   val memdelay = Module(new AXI4Delayer(0))