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/sbc8548/ddr.c b/board/sbc8548/ddr.c
index f7af1e3..61bc77c 100644
--- a/board/sbc8548/ddr.c
+++ b/board/sbc8548/ddr.c
@@ -5,6 +5,7 @@
 
 #include <common.h>
 #include <i2c.h>
+#include <linux/delay.h>
 
 #include <fsl_ddr_sdram.h>
 #include <fsl_ddr_dimm_params.h>