common: Move get_tbclk() to time.h

This function related to timer and most of the timer functions are in
time.h, so move this function there.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc83xx/spl_minimal.c b/arch/powerpc/cpu/mpc83xx/spl_minimal.c
index 75b03f3..34c8187 100644
--- a/arch/powerpc/cpu/mpc83xx/spl_minimal.c
+++ b/arch/powerpc/cpu/mpc83xx/spl_minimal.c
@@ -6,6 +6,7 @@
 #include <common.h>
 #include <clock_legacy.h>
 #include <mpc83xx.h>
+#include <time.h>
 
 #include "lblaw/lblaw.h"
 #include "elbc/elbc.h"