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/chiliboard_defconfig b/configs/chiliboard_defconfig
index 1b08e75..9c3fe8e 100644
--- a/configs/chiliboard_defconfig
+++ b/configs/chiliboard_defconfig
@@ -24,6 +24,7 @@
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
+CONFIG_SPL_NAND_BASE=y
 CONFIG_SPL_POWER_SUPPORT=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_CMD_ASKENV=y