sc520: Allow boards to override udelay

If the board has a high precision mico-second timer, it maked sense to use
it instead of the on-chip one

Signed-off-by: Graeme Russ <graeme.russ@gmail.com>

arch/i386/cpu/sc520/sc520_timer.c

@@ -69,7 +69,11 @@ int timer_init(void)
 	return 0;
 }
 
+/* Allow boards to override udelay implementation */
 void __udelay(unsigned long usec)
+	__attribute__((weak, alias("sc520_udelay")));
+
+void sc520_udelay(unsigned long usec)
 {
 	int m = 0;
 	long u;

arch/i386/include/asm/ic/sc520.h

@@ -28,6 +28,7 @@
 
 void init_sc520(void);
 unsigned long init_sc520_dram(void);
+void sc520_udelay(unsigned long usec);
 
 /* Memory mapped configuration registers */
 typedef struct sc520_mmcr {