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/devkit8000_defconfig b/configs/devkit8000_defconfig
index a57b78d..4eae268 100644
--- a/configs/devkit8000_defconfig
+++ b/configs/devkit8000_defconfig
@@ -9,6 +9,9 @@
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_ECC=y
+CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_SPL_OS_BOOT=y
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_SPL=y
@@ -34,6 +37,5 @@
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y
-CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_CONS_INDEX=3
 CONFIG_OF_LIBFDT=y