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/drivers/clk/clk_pic32.c b/drivers/clk/clk_pic32.c
index b3ac0d5..79469c4 100644
--- a/drivers/clk/clk_pic32.c
+++ b/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>