[PGO] internal option cleanups

1. Added comments for options
2. Added missing option cl::desc field
3. Uniified function filter option for graph viewing.
   Now PGO count/raw-counts share the same
   filter option: -view-bfi-func-name=.

llvm-svn: 293938
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 8128efb..024d41f 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -160,7 +160,13 @@
 extern cl::opt<unsigned> StaticLikelyProb;
 extern cl::opt<unsigned> ProfileLikelyProb;
 
+// Internal option used to control BFI display only after MBP pass.
+// Defined in CodeGen/MachineBlockFrequencyInfo.cpp:
+// -view-block-layout-with-bfi=
 extern cl::opt<GVDAGType> ViewBlockLayoutWithBFI;
+
+// Command line option to specify the name of the function for CFG dump
+// Defined in Analysis/BlockFrequencyInfo.cpp:  -view-bfi-func-name=
 extern cl::opt<std::string> ViewBlockFreqFuncName;
 
 namespace {