sched/cputime: Convert task/group cputime to nsecs

Now that most cputime readers use the transition API which return the
task cputime in old style cputime_t, we can safely store the cputime in
nsecs. This will eventually make cputime statistics less opaque and more
granular. Back and forth convertions between cputime_t and nsecs in order
to deal with cputime_t random granularity won't be needed anymore.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1485832191-26889-8-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/exit.c b/kernel/exit.c
index 8f14b86..8e5e213 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -86,7 +86,7 @@ static void __exit_signal(struct task_struct *tsk)
 	bool group_dead = thread_group_leader(tsk);
 	struct sighand_struct *sighand;
 	struct tty_struct *uninitialized_var(tty);
-	cputime_t utime, stime;
+	u64 utime, stime;
 
 	sighand = rcu_dereference_check(tsk->sighand,
 					lockdep_tasklist_lock_is_held());
@@ -1091,7 +1091,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 		struct signal_struct *sig = p->signal;
 		struct signal_struct *psig = current->signal;
 		unsigned long maxrss;
-		cputime_t tgutime, tgstime;
+		u64 tgutime, tgstime;
 
 		/*
 		 * The resource counters for the group leader are in its