cpu: Move the branch predictor out of the BaseCPU

The branch predictor is guarded by having either the in-order or
out-of-order CPU as one of the available CPU models and therefore
should not be used in the BaseCPU. This patch moves the parameter to
the relevant CPU classes.

src/cpu/o3/O3CPU.py

@@ -125,7 +125,9 @@ class DerivO3CPU(BaseCPU):
     smtROBThreshold = Param.Int(100, "SMT ROB Threshold Sharing Parameter")
     smtCommitPolicy = Param.String('RoundRobin', "SMT Commit Policy")
 
-    branchPred = BranchPredictor(numThreads = Parent.numThreads)
+    branchPred = Param.BranchPredictor(BranchPredictor(numThreads =
+                                                       Parent.numThreads),
+                                       "Branch Predictor")
     needsTSO = Param.Bool(buildEnv['TARGET_ISA'] == 'x86',
                           "Enable TSO Memory model")