[block-freq] Convert BlockFrequencyImpl to use the new printing functionality from r197285.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197286 91177308-0d34-0410-b5e6-96231b3b80d8
[block-freq] Add the equivalent methods to MachineBlockFrequencyInfo and BlockFrequencyInfo that were added to BlockFrequencyImpl in r197285 and r197284.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197287 91177308-0d34-0410-b5e6-96231b3b80d8