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/mpc85xx/interrupts.c b/arch/powerpc/cpu/mpc85xx/interrupts.c
index e767573..6f539d2 100644
--- a/arch/powerpc/cpu/mpc85xx/interrupts.c
+++ b/arch/powerpc/cpu/mpc85xx/interrupts.c
@@ -12,6 +12,7 @@
 
 #include <common.h>
 #include <irq_func.h>
+#include <time.h>
 #include <watchdog.h>
 #include <command.h>
 #include <asm/processor.h>