[POWERPC] bootwrapper: Set timebase_period_ns from dt_fixup_cpu_clocks

This lets udelay() work properly on platforms which use dt_fixup_cpu_clocks.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
index 8607706..aebd6ed 100644
--- a/arch/powerpc/boot/ops.h
+++ b/arch/powerpc/boot/ops.h
@@ -191,4 +191,6 @@
 	static char _bss_stack[size]; \
 	void *_platform_stack_top = _bss_stack + sizeof(_bss_stack);
 
+extern unsigned long timebase_period_ns;
+
 #endif /* _PPC_BOOT_OPS_H_ */