common: Move get_ticks() function out of common.h

This function belongs in time.h so move it over and add a comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/time.h b/include/time.h
index 875a2b2..71446c3 100644
--- a/include/time.h
+++ b/include/time.h
@@ -103,4 +103,14 @@
  */
 unsigned long timer_get_us(void);
 
+/**
+ * get_ticks() - Get the current tick value
+ *
+ * This is an internal value used by the timer on the system. Ticks increase
+ * monotonically at the rate given by get_tbclk().
+ *
+ * @return current tick value
+ */
+uint64_t get_ticks(void);
+
 #endif /* _TIME_H */