Convert CONFIG_SPL_NAND_DRIVERS et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_NAND_DRIVERS
   CONFIG_SPL_NAND_ECC
   CONFIG_SPL_NAND_SIMPLE

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/smartweb_defconfig b/configs/smartweb_defconfig
index 977d2bd..7bdd8f0 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -23,6 +23,8 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_NAND_SUPPORT=y
+CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_ECC=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot# "
 CONFIG_AUTOBOOT_KEYED=y