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/common/spl/Kconfig b/common/spl/Kconfig
index 1a5cf13..dcc1a95 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -752,6 +752,18 @@
 	  Support for NAND boot using simple NAND drivers that
 	  expose the cmd_ctrl() interface.
 
+config SPL_NAND_BASE
+	depends on SPL_NAND_DRIVERS
+	bool "Use Base NAND Driver"
+        help
+          Include nand_base.c in the SPL.
+
+config SPL_NAND_IDENT
+	depends on SPL_NAND_BASE
+	bool "Use chip ID to identify NAND flash"
+	help
+	  SPL uses the chip ID list to identify the NAND flash.
+
 config SPL_UBI
 	bool "Support UBI"
 	help