Convert CONFIG_NAND_DAVINCI to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND_DAVINCI

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 8175fbb..1e4ea7b 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -16,6 +16,12 @@
 	  Enable this driver for NAND flash platforms using an Atmel NAND
 	  controller.
 
+config NAND_DAVINCI
+	bool "Support TI Davinci NAND controller"
+	help
+	  Enable this driver for NAND flash controllers available in TI Davinci
+	  and Keystone2 platforms
+
 config NAND_DENALI
 	bool
 	select SYS_NAND_SELF_INIT