kfdtest: limit vram allocation size for MigrateAccessInPlaceTest

On the some platform there's only 256MB vram and then will fail to
allocate 256MB vram. So let's limit a small vram allocation for
ensuring vram allocated successfully.

Change-Id: Iba4c469de56925675e5624b300a6153e24ab19b3
Signed-off-by: Prike Liang <Prike.Liang@amd.com>

tests/kfdtest/src/KFDSVMRangeTest.cpp

@@ -690,7 +690,7 @@ TEST_F(KFDSVMRangeTest, MigrateAccessInPlaceTest) {
         return;
     }
 
-    unsigned int BufferSize = 256 << 20;
+    unsigned int BufferSize = MIN(256ULL << 20, GetVramSize(defaultGPUNode) / 2);
     SDMAQueue sdmaQueue;
     ASSERT_SUCCESS(sdmaQueue.Create(defaultGPUNode));