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/omap3_beagle_defconfig b/configs/omap3_beagle_defconfig
index 1f40d81..020e58d 100644
--- a/configs/omap3_beagle_defconfig
+++ b/configs/omap3_beagle_defconfig
@@ -23,6 +23,7 @@
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
 CONFIG_SPL_NAND_SIMPLE=y
+CONFIG_SPL_NAND_BASE=y
 CONFIG_SYS_PROMPT="BeagleBoard # "
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_NAND_OFS=0x280000