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/omap3_evm_defconfig b/configs/omap3_evm_defconfig
index 9b252c3..3c0d5fe 100644
--- a/configs/omap3_evm_defconfig
+++ b/configs/omap3_evm_defconfig
@@ -18,6 +18,9 @@
 CONFIG_SPL_SEPARATE_BSS=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_SYS_PROMPT="OMAP3_EVM # "
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_NAND_OFS=0x280000
@@ -60,7 +63,6 @@
 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_SMC911X=y
 CONFIG_SMC911X_BASE=0x2C000000
 CONFIG_SMC911X_32_BIT=y