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/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index 9d4be2a..bc1f7c8 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -13,7 +13,6 @@
 CONFIG_SPL_FAT_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="dm8168-evm"
 CONFIG_DISTRO_DEFAULTS=y
-CONFIG_SYS_EXTRA_OPTIONS="NAND"
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_BOOTDELAY=3
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
@@ -41,5 +40,6 @@
 CONFIG_DM_I2C=y
 CONFIG_SYS_I2C_OMAP24XX=y
 CONFIG_MMC_OMAP_HS=y
+CONFIG_NAND=y
 CONFIG_SYS_NS16550=y
 # CONFIG_USE_PRIVATE_LIBGCC is not set