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/spear310_usbtty_nand_defconfig b/configs/spear310_usbtty_nand_defconfig
index ed2b7b0..b8bb8b4 100644
--- a/configs/spear310_usbtty_nand_defconfig
+++ b/configs/spear310_usbtty_nand_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_TARGET_SPEAR310=y
 CONFIG_IDENT_STRING="-SPEAr"
-CONFIG_SYS_EXTRA_OPTIONS="SPEAR310,USBTTY,NAND"
+CONFIG_SYS_EXTRA_OPTIONS="SPEAR310,USBTTY"
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_BOOTDELAY=-1
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
@@ -15,6 +15,7 @@
 CONFIG_SYS_I2C_DW=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
+CONFIG_NAND=y
 CONFIG_NETDEVICES=y
 CONFIG_PHY_GIGE=y
 CONFIG_ETH_DESIGNWARE=y