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/arch/microblaze/cpu/timer.c b/arch/microblaze/cpu/timer.c
index 58e5c30..805eac7 100644
--- a/arch/microblaze/cpu/timer.c
+++ b/arch/microblaze/cpu/timer.c
@@ -7,6 +7,7 @@
 
 #include <common.h>
 #include <fdtdec.h>
+#include <time.h>
 #include <asm/microblaze_timer.h>
 #include <asm/microblaze_intc.h>