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/am335x_baltos_defconfig b/configs/am335x_baltos_defconfig
index 180268e..41ca490 100644
--- a/configs/am335x_baltos_defconfig
+++ b/configs/am335x_baltos_defconfig
@@ -14,7 +14,6 @@
 CONFIG_SPL_FAT_SUPPORT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
-CONFIG_SYS_EXTRA_OPTIONS="NAND"
 CONFIG_ENV_IS_NOWHERE=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_VERSION_VARIABLE=y
@@ -53,6 +52,7 @@
 CONFIG_ISO_PARTITION=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_PHYLIB=y
+CONFIG_NAND=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_MUSB_HOST=y