proc: Consolidate task->comm formatting into proc_task_name()

proc shows task->comm in three places - comm, stat, status - and each
is fetching and formatting task->comm slighly differently.  This patch
renames task_name() to proc_task_name(), makes it more generic, and
updates all three paths to use it.

This will enable expanding comm reporting for workqueue workers.

Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 0f1692e..b823fac62 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -131,6 +131,8 @@ unsigned name_to_int(const struct qstr *qstr);
  */
 extern const struct file_operations proc_tid_children_operations;
 
+extern void proc_task_name(struct seq_file *m, struct task_struct *p,
+			   bool escape);
 extern int proc_tid_stat(struct seq_file *, struct pid_namespace *,
 			 struct pid *, struct task_struct *);
 extern int proc_tgid_stat(struct seq_file *, struct pid_namespace *,