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/work_92105_defconfig b/configs/work_92105_defconfig
index e884cf7..10694f4 100644
--- a/configs/work_92105_defconfig
+++ b/configs/work_92105_defconfig
@@ -27,6 +27,7 @@
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_NAND_DRIVERS=y
+CONFIG_SPL_NAND_BASE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_EEPROM=y
 # CONFIG_CMD_FLASH is not set