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>

drivers/clk/clk_pic32.c

@@ -8,6 +8,7 @@
 #include <clk-uclass.h>
 #include <dm.h>
 #include <div64.h>
+#include <time.h>
 #include <wait_bit.h>
 #include <dm/lists.h>
 #include <asm/io.h>