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/twister_defconfig b/configs/twister_defconfig
index 29c183a..db26be1 100644
--- a/configs/twister_defconfig
+++ b/configs/twister_defconfig
@@ -30,6 +30,7 @@
 CONFIG_CMD_FAT=y
 CONFIG_CMD_UBI=y
 CONFIG_MMC_OMAP_HS=y
+CONFIG_NAND=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y