arm: Move timer_rate_hz into arch_global_data

Move this field into arch_global_data and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/arm920t/s3c24x0/timer.c b/arch/arm/cpu/arm920t/s3c24x0/timer.c
index d8668be..7694fea 100644
--- a/arch/arm/cpu/arm920t/s3c24x0/timer.c
+++ b/arch/arm/cpu/arm920t/s3c24x0/timer.c
@@ -52,7 +52,7 @@
 		 * @33.25MHz and 15625 @ 50 MHz
 		 */
 		gd->tbu = get_PCLK() / (2 * 16 * 100);
-		gd->timer_rate_hz = get_PCLK() / (2 * 16);
+		gd->arch.timer_rate_hz = get_PCLK() / (2 * 16);
 	}
 	/* load value for 10 ms timeout */
 	writel(gd->tbu, &timers->tcntb4);
@@ -93,7 +93,7 @@
 {
 	ulong tmr = get_ticks();
 
-	return tmr / (gd->timer_rate_hz / CONFIG_SYS_HZ);
+	return tmr / (gd->arch.timer_rate_hz / CONFIG_SYS_HZ);
 }
 
 void udelay_masked(unsigned long usec)