common: Drop linux/delay.h from common header

Move this uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/serial_stm32.c b/drivers/serial/serial_stm32.c
index a9f5c3c..5c1cf81 100644
--- a/drivers/serial/serial_stm32.c
+++ b/drivers/serial/serial_stm32.c
@@ -13,6 +13,7 @@
 #include <watchdog.h>
 #include <asm/io.h>
 #include <asm/arch/stm32.h>
+#include <linux/delay.h>
 #include "serial_stm32.h"
 #include <dm/device_compat.h>