Convert CONFIG_NAND to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Sync up a few more, add imply's]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/CHIP_pro_defconfig b/configs/CHIP_pro_defconfig
index f9033bc..2d0a9aa 100644
--- a/configs/CHIP_pro_defconfig
+++ b/configs/CHIP_pro_defconfig
@@ -20,6 +20,7 @@
 CONFIG_MTDIDS_DEFAULT="nand0=sunxi-nand.0"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=sunxi-nand.0:256k(spl),256k(spl-backup),2m(uboot),2m(uboot-backup),-(UBI)"
 # CONFIG_MMC is not set
+CONFIG_NAND=y
 CONFIG_NAND_SUNXI=y
 CONFIG_AXP_ALDO3_VOLT=3300
 CONFIG_AXP_ALDO4_VOLT=3300