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/arm/mach-versal/clk.c b/arch/arm/mach-versal/clk.c
index b82cea4..9184714 100644
--- a/arch/arm/mach-versal/clk.c
+++ b/arch/arm/mach-versal/clk.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <time.h>
 
 DECLARE_GLOBAL_DATA_PTR;