kfdtest: Split BigBufferStressTest into two smaller tests

The previous BigBufferStressTest has too much stuff and takes a long
time to run. By separating largest*BufferTest out into other
tests, we dramatically reduce the time to run BigBufferStressTest and
therefore make reproducing issues much easier.

Meanwhile, rename the test to BigSysBufferStressTest to express more
information.

Change-Id: I5911f113c0bd50627ee6d84bbb4f2972cbed8886
Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>

tests/kfdtest/scripts/kfdtest.exclude

@@ -110,12 +110,13 @@ FILTER[kaveri]=\
 "KFDQMTest.CpuWriteCoherence"
 
 # KFDLocalMemoryTest.BasicTest is failing intermittently (KFD-368)
-# KFDMemoryTest.BigBufferStressTest was failing intermittently on 4.9 and hangs when executed twice (KFD-312)
+# KFDMemoryTest.BigSysBufferStressTest was failing intermittently on 4.9
+# and hangs when executed twice (KFD-312)
 # KFDQMTest.GPUDoorbellWrite fails on Hawaii. Could be HW-related (KFD-342)
 FILTER[hawaii]=\
 "$BLACKLIST_ALL_ASICS:"\
 "KFDLocalMemoryTest.BasicTest:"\
-"KFDMemoryTest.BigBufferStressTest:"\
+"KFDMemoryTest.BigSysBufferStressTest:"\
 "KFDQMTest.GPUDoorbellWrite"
 
 FILTER[carrizo]=\