ARM: convert arm/arm64 arch timer to use CLKSRC_OF init

This converts arm and arm64 to use CLKSRC_OF DT based initialization for
the arch timer. A new function arch_timer_arch_init is added to allow for
arch specific setup.

This has a side effect of enabling sched_clock on omap5 and exynos5. There
should not be any reason not to use the arch timers for sched_clock.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-omap@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm64/kernel/time.c

@@ -32,6 +32,7 @@
 #include <linux/timer.h>
 #include <linux/irq.h>
 #include <linux/delay.h>
+#include <linux/clocksource.h>
 
 #include <clocksource/arm_arch_timer.h>
 
@@ -77,10 +78,11 @@ void __init time_init(void)
 {
 	u32 arch_timer_rate;
 
-	if (arch_timer_init())
-		panic("Unable to initialise architected timer.\n");
+	clocksource_of_init();
 
 	arch_timer_rate = arch_timer_get_rate();
+	if (!arch_timer_rate)
+		panic("Unable to initialise architected timer.\n");
 
 	/* Cache the sched_clock multiplier to save a divide in the hot path. */
 	sched_clock_mult = NSEC_PER_SEC / arch_timer_rate;