Convert CONFIG_NAND to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Sync up a few more, add imply's]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 3508c62..71d678f 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -1,4 +1,7 @@
-menu "NAND Device Support"
+
+menuconfig NAND
+	bool "NAND Device Support"
+if NAND
 
 config SYS_NAND_SELF_INIT
 	bool
@@ -173,4 +176,4 @@
 
 endif
 
-endmenu
+endif   # if NAND