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>

tools/perf/util/callchain.c

@@ -1577,3 +1577,18 @@ int callchain_cursor__copy(struct callchain_cursor *dst,
 
 	return rc;
 }
+
+/*
+ * Initialize a cursor before adding entries inside, but keep
+ * the previously allocated entries as a cache.
+ */
+void callchain_cursor_reset(struct callchain_cursor *cursor)
+{
+	struct callchain_cursor_node *node;
+
+	cursor->nr = 0;
+	cursor->last = &cursor->first;
+
+	for (node = cursor->first; node != NULL; node = node->next)
+		map__zput(node->map);
+}