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/brppt1_nand_defconfig b/configs/brppt1_nand_defconfig
index fff4103..afe2031 100644
--- a/configs/brppt1_nand_defconfig
+++ b/configs/brppt1_nand_defconfig
@@ -34,6 +34,7 @@
 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_SPL_YMODEM_SUPPORT=y