perf callchain: Uninline callchain_cursor_reset() to remove map.h dependency

perf callchain: Uninline callchain_cursor_reset() to remove map.h dependency

That was the only thing that made including map.h in callchain.h a
requiriment, so uninline it and just add a 'struct map' forward
declaration.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-7fjz4hvv1bpzqaeriku44fn4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>