[S390] cputime: add sparse checking and cleanup

Make cputime_t and cputime64_t nocast to enable sparse checking to
detect incorrect use of cputime. Drop the cputime macros for simple
scalar operations. The conversion macros are still needed.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 87f9e36..4b71dbe 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -283,8 +283,7 @@
 		return;
 
 	raw_spin_lock(&cputimer->lock);
-	cputimer->cputime.utime =
-		cputime_add(cputimer->cputime.utime, cputime);
+	cputimer->cputime.utime += cputime;
 	raw_spin_unlock(&cputimer->lock);
 }
 
@@ -307,8 +306,7 @@
 		return;
 
 	raw_spin_lock(&cputimer->lock);
-	cputimer->cputime.stime =
-		cputime_add(cputimer->cputime.stime, cputime);
+	cputimer->cputime.stime += cputime;
 	raw_spin_unlock(&cputimer->lock);
 }