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/igep00x0_defconfig b/configs/igep00x0_defconfig
index 5be725a..1bc36ca 100644
--- a/configs/igep00x0_defconfig
+++ b/configs/igep00x0_defconfig
@@ -18,6 +18,9 @@
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 # CONFIG_SPL_FS_EXT4 is not set
 CONFIG_SPL_MTD_SUPPORT=y
+CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_ECC=y
+CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_SPL_UBI=y
 CONFIG_SPL_UBI_MAX_VOL_LEBS=256
 CONFIG_SPL_UBI_MAX_PEB_SIZE=262144
@@ -56,7 +59,6 @@
 CONFIG_SYS_MTDPARTS_RUNTIME=y
 CONFIG_MTD_RAW_NAND=y
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y
-CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_SMC911X=y
 CONFIG_SMC911X_BASE=0x2C000000