perf: Implement lbr-as-callgraph v2

[Andi Kleen <andi@firstfloor.org>]

This patchkit implements lbr-as-callgraphs in per freport,
as an alternative way to present LBR information.

Current perf report does a histogram over the branch edges,
which is useful to look at basic blocks, but doesn't tell
you anything about the larger control flow.

This patchkit adds a new option --branch-history that
adds the branch paths to the callgraph history instead.

This allows to reason about individual branch paths leading
to specific samples.

Updates to v1:
- rebased on perf/core
- fix various issues
- rename the option to --branch-history
- various fixes to display the information more concise

Example output:

    % perf record -b -g ./tsrc/tcall
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.044 MB perf.data (~1923 samples) ]
    % perf report --branch-history
    ...
        54.91%  tcall.c:6  [.] f2                      tcall
                |
                |--66.53%-- f2 tcall.c:5
                |          |
                |          |--70.83%-- f1 tcall.c:11
                |          |          f1 tcall.c:10
                |          |          main tcall.c:18
                |          |          main tcall.c:18
                |          |          main tcall.c:17
                |          |          main tcall.c:17
                |          |          f1 tcall.c:13
                |          |          f1 tcall.c:13
                |          |          f2 tcall.c:7
                |          |          f2 tcall.c:5
                |          |          f1 tcall.c:12
                |          |          f1 tcall.c:12
                |          |          f2 tcall.c:7
                |          |          f2 tcall.c:5
                |          |          f1 tcall.c:11