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>
diff --git a/arch/i386/include/asm/ic/sc520.h b/arch/i386/include/asm/ic/sc520.h
index 57c9904..20384a4 100644
--- a/arch/i386/include/asm/ic/sc520.h
+++ b/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 {