ARM: make machine_desc->init_time default to clocksource_of_init

Originally from a default machine descriptor patch from Arnd, pull out
just the default call to clocksource_of_init part. This is needed so that
platforms can simply remove .init_time calls as they are converted to use
clocksource_of_init.

Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Nicolas Pitre <[e-mail]>
Acked-by: Olof Johansson <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

arch/arm/kernel/time.c

···
 #include <linux/errno.h>
 #include <linux/profile.h>
 #include <linux/timer.h>
+#include <linux/clocksource.h>
 #include <linux/irq.h>
 
 #include <asm/thread_info.h>
···
 
 void __init time_init(void)
 {
-	machine_desc->init_time();
+	if (machine_desc->init_time)
+		machine_desc->init_time();
+	else
+		clocksource_of_init();
+
 	sched_clock_postinit();
 }