ARM: orion: implement ARM delay timer

Implement an ARM delay timer to be used for udelay() on orion legacy
platforms. This allows us to skip the delay loop calibration at boot.

It also means that udelay() will be unaffected by CPU frequency changes
when cpufreq is enabled on these platforms.

Tested-by: Russell King <[e-mail]>
Acked-by: Andrew Lunn <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/plat-orion/time.c

···
 #include <linux/irq.h>
 #include <linux/sched_clock.h>
 #include <plat/time.h>
+#include <asm/delay.h>
 
 /*
  * MBus bridge block registers.
···
 	timer_base = _timer_base;
 }
 
+static unsigned long orion_delay_timer_read(void)
+{
+	return ~readl(timer_base + TIMER0_VAL_OFF);
+}
+
+static struct delay_timer orion_delay_timer = {
+	.read_current_timer = orion_delay_timer_read,
+};
+
 void __init
 orion_time_init(void __iomem *_bridge_base, u32 _bridge_timer1_clr_mask,
 		unsigned int irq, unsigned int tclk)
···
 	bridge_timer1_clr_mask = _bridge_timer1_clr_mask;
 
 	ticks_per_jiffy = (tclk + HZ/2) / HZ;
+
+	orion_delay_timer.freq = tclk;
+	register_current_timer_delay(&orion_delay_timer);
 
 	/*
 	 * Set scale and timer for sched_clock.