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/devkit3250_defconfig b/configs/devkit3250_defconfig
index 8584c0e..7130d06 100644
--- a/configs/devkit3250_defconfig
+++ b/configs/devkit3250_defconfig
@@ -21,6 +21,9 @@
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_NAND_SUPPORT=y
+CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_ECC=y
+CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y
@@ -44,7 +47,6 @@
 CONFIG_MTD_RAW_NAND=y
 CONFIG_SYS_NAND_USE_FLASH_BBT=y
 CONFIG_NAND_LPC32XX_SLC=y
-CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_ADDR_ENABLE=y
 CONFIG_PHY_ADDR=31