perf header: Add ability to keep feature sections

Many feature sections should not be re-written during perf inject. In
preparation to support that, add callbacks that a tool can use to copy
a feature section from elsewhere. perf inject will use this facility to
copy features sections from the input file.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220520132404.25853-2-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>