sched/clock: Move sched clock initialization and merge with generic clock

sched_clock_postinit() initializes a generic clock on systems where no
other clock is provided. This function may be called only after
timekeeping_init().

Rename sched_clock_postinit to generic_clock_inti() and call it from
sched_clock_init(). Move the call for sched_clock_init() until after
time_init().

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-23-pasha.tatashin@oracle.com

init/main.c

@@ -79,7 +79,7 @@
 #include <linux/pti.h>
 #include <linux/blkdev.h>
 #include <linux/elevator.h>
-#include <linux/sched_clock.h>
+#include <linux/sched/clock.h>
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/context_tracking.h>
@@ -642,7 +642,7 @@ asmlinkage __visible void __init start_kernel(void)
 	softirq_init();
 	timekeeping_init();
 	time_init();
-	sched_clock_postinit();
+	sched_clock_init();
 	printk_safe_init();
 	perf_event_init();
 	profile_init();