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/tao3530_defconfig b/configs/tao3530_defconfig
index b3074ce..4f57b0f 100644
--- a/configs/tao3530_defconfig
+++ b/configs/tao3530_defconfig
@@ -8,6 +8,9 @@
 CONFIG_SPL=y
 CONFIG_BOOTDELAY=3
 # CONFIG_SPL_FS_EXT4 is not set
+CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_ECC=y
+CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="TAO-3530 # "
 # CONFIG_CMD_IMI is not set
@@ -32,7 +35,6 @@
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y
-CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_CONS_INDEX=3
 CONFIG_SYS_NS16550=y
 CONFIG_SPI=y