Adds latency tracer support for ep93xx platform.

Signed-off-by: Luotao Fu <lfu@pengutronix.de>

Index: linux-2.6.18-rt.sec/include/asm-arm/arch-ep93xx/timex.h
===================================================================
--- include/asm-arm/arch-ep93xx/timex.h
+++ include/asm-arm/arch-ep93xx/timex.h
@@ -3,3 +3,10 @@
  */
 
 #define CLOCK_TICK_RATE		983040
+
+#include <asm/io.h>
+#include <asm-arm/arch-ep93xx/ep93xx-regs.h>
+
+#define mach_read_cycles() readl(EP93XX_TIMER4_VALUE_LOW)
+#define mach_cycles_to_usecs(d) (((d) * ((1000000LL << 32) / CLOCK_TICK_RATE)) >> 32)
+#define mach_usecs_to_cycles(d) (((d) * (((long long)CLOCK_TICK_RATE << 32) / 1000000)) >> 32)