Convert CONFIG_NAND_ATMEL to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND_ATMEL

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/pm9g45_defconfig b/configs/pm9g45_defconfig
index 2a59ff3..99acd20 100644
--- a/configs/pm9g45_defconfig
+++ b/configs/pm9g45_defconfig
@@ -21,5 +21,7 @@
 CONFIG_CMD_JFFS2=y
 CONFIG_ENV_IS_IN_NAND=y
 # CONFIG_MMC is not set
+CONFIG_NAND=y
+CONFIG_NAND_ATMEL=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y