arm: vf610: add NAND support for vf610twr

This adds NAND support for the Vybrid tower system (TWR-VF65GS10)
provided by the vf610_nfc driver. Full 16-Bit bus width is
supported. Also an aditional config vf610twr_nand is introduced
which gets the environment from NAND. However, booting U-Boot from
NAND is not yet possible due to missing boot configuration block
(BCB).

Signed-off-by: Stefan Agner <stefan@agner.ch>
diff --git a/configs/vf610twr_defconfig b/configs/vf610twr_defconfig
index 10e6432..7de374a 100644
--- a/configs/vf610twr_defconfig
+++ b/configs/vf610twr_defconfig
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/vf610twr/imximage.cfg"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/vf610twr/imximage.cfg,ENV_IS_IN_MMC"
 CONFIG_ARM=y
 CONFIG_TARGET_VF610TWR=y