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/omap35_logic_defconfig b/configs/omap35_logic_defconfig
index 66933a1..30d11f0 100644
--- a/configs/omap35_logic_defconfig
+++ b/configs/omap35_logic_defconfig
@@ -26,6 +26,9 @@
 # CONFIG_SPL_FS_EXT4 is not set
 # CONFIG_SPL_I2C_SUPPORT 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_OS_BOOT=y
 CONFIG_SYS_PROMPT="OMAP Logic # "
 # CONFIG_CMD_IMI is not set
@@ -56,7 +59,6 @@
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y
 CONFIG_SYS_NAND_U_BOOT_LOCATIONS=y
 CONFIG_SYS_NAND_U_BOOT_OFFS=0x80000
-CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_DM_ETH=y
 CONFIG_SMC911X=y
 CONFIG_SMC911X_32_BIT=y