mem-ruby: Always pass on GPU atomics to dir in write-through TCC (#367)

Added checks to ensure that atomics are not performed in the TCC when it
is configured as a write-through cache. Also added SLC bit overwrite to
ensure directory preforms atomics when there is a write-through TCC.

Change-Id: I4514e6c8022aeb7785f2c59871cd9acec8161ed8

configs/ruby/GPU_VIPER.py

@@ -555,6 +555,7 @@ def construct_dirs(options, system, ruby_system, network):
         dir_cntrl.create(options, dir_ranges, ruby_system, system)
         dir_cntrl.number_of_TBEs = options.num_tbes
         dir_cntrl.useL3OnWT = options.use_L3_on_WT
+        dir_cntrl.L2isWB = options.WB_L2
         # the number_of_TBEs is inclusive of TBEs below
 
         # Connect the Directory controller to the ruby network