s390/time: refactor clock sync

Merge clock_sync_cpu into stp_sync_clock and split out the update
of the global and per-CPU clock fields into clock_sync_global
and clock_sync_local.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/early.c

@@ -467,7 +467,7 @@ void __init startup_init(void)
 	ipl_save_parameters();
 	rescue_initrd();
 	clear_bss_section();
-	ptff_init();
+	time_early_init();
 	init_kernel_storage_key();
 	lockdep_off();
 	setup_lowcore_early();