[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/tsacct.c b/kernel/tsacct.c
index 5bbfac8..23b4d78 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -127,7 +127,7 @@
 
 		local_irq_save(flags);
 		time = tsk->stime + tsk->utime;
-		dtime = cputime_sub(time, tsk->acct_timexpd);
+		dtime = time - tsk->acct_timexpd;
 		jiffies_to_timeval(cputime_to_jiffies(dtime), &value);
 		delta = value.tv_sec;
 		delta = delta * USEC_PER_SEC + value.tv_usec;