Convert CONFIG_SPL_NAND_BASE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_NAND_BASE
   CONFIG_SPL_NAND_IDENT

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/igep00x0_defconfig b/configs/igep00x0_defconfig
index 1bc36ca..3a3f0d0 100644
--- a/configs/igep00x0_defconfig
+++ b/configs/igep00x0_defconfig
@@ -21,6 +21,7 @@
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
 CONFIG_SPL_NAND_SIMPLE=y
+CONFIG_SPL_NAND_BASE=y
 CONFIG_SPL_UBI=y
 CONFIG_SPL_UBI_MAX_VOL_LEBS=256
 CONFIG_SPL_UBI_MAX_PEB_SIZE=262144