On ARM the debug info is not present in the .eh_frame sections but
in .debug_frame instead, in dwarf format.
Use libunwind to load and parse the debug info.

Dependencies:
 . if present, libunwind >= 1.1 is needed to prevent a segfault when
   parsing the dwarf info,
 . libunwind needs to be configured with --enable-debug-frame. Note:
   --enable-debug-frame is automatically selected on ARM.
Acked-by: NJiri Olsa <jolsa@redhat.com>
Signed-off-by: NJean Pihet <jean.pihet@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>