driver/ddr: Add 256 byte interleaving support

Freescale LayerScape SoCs support controller interleaving on 256 byte size.
This interleaving is mandoratory.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/drivers/ddr/fsl/main.c b/drivers/ddr/fsl/main.c
index dee50a0..d62ca63 100644
--- a/drivers/ddr/fsl/main.c
+++ b/drivers/ddr/fsl/main.c
@@ -291,6 +291,7 @@
 		for (i = 0; i < CONFIG_NUM_DDR_CONTROLLERS; i++) {
 			if (pinfo->memctl_opts[i].memctl_interleaving) {
 				switch (pinfo->memctl_opts[i].memctl_interleaving_mode) {
+				case FSL_DDR_256B_INTERLEAVING:
 				case FSL_DDR_CACHE_LINE_INTERLEAVING:
 				case FSL_DDR_PAGE_INTERLEAVING:
 				case FSL_DDR_BANK_INTERLEAVING: