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/board/gardena/smart-gateway-mt7688/board.c b/board/gardena/smart-gateway-mt7688/board.c
index a75bb1f..8a3a6e3 100644
--- a/board/gardena/smart-gateway-mt7688/board.c
+++ b/board/gardena/smart-gateway-mt7688/board.c
@@ -15,6 +15,7 @@
 #include <net.h>
 #include <spi.h>
 #include <spi_flash.h>
+#include <linux/delay.h>
 #include <linux/stringify.h>
 #include <u-boot/crc.h>
 #include <uuid.h>