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/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index dad5711..8175fbb 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -9,6 +9,13 @@
 	  This option, if enabled, provides more flexible and linux-like
 	  NAND initialization process.
 
+config NAND_ATMEL
+	bool "Support Atmel NAND controller"
+	imply SYS_NAND_USE_FLASH_BBT
+	help
+	  Enable this driver for NAND flash platforms using an Atmel NAND
+	  controller.
+
 config NAND_DENALI
 	bool
 	select SYS_NAND_SELF_INIT