Convert CONFIG_SYS_FSL_DDR_INTLV_256B to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FSL_DDR_INTLV_256B

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/lx2160ardb_tfa_stmm_defconfig b/configs/lx2160ardb_tfa_stmm_defconfig
index c7e9afe..547c868 100644
--- a/configs/lx2160ardb_tfa_stmm_defconfig
+++ b/configs/lx2160ardb_tfa_stmm_defconfig
@@ -67,6 +67,7 @@
 CONFIG_DIMM_SLOTS_PER_CTLR=2
 CONFIG_DDR_ECC=y
 CONFIG_ECC_INIT_VIA_DDRCONTROLLER=y
+CONFIG_SYS_FSL_DDR_INTLV_256B=y
 CONFIG_MPC8XXX_GPIO=y
 CONFIG_DM_I2C=y
 CONFIG_I2C_SET_DEFAULT_BUS_NUM=y