perf annotate: Add annotation_line struct

In order to make the annotation support generic, addadding 'struct
annotation_line', which will hold generic data common to annotation
sources (such as the one for python scripts, coming on upcoming
patches).

Having this, we can add different annotation line support other than
objdump disasm.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171011150158.11895-3-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>