mtd: kconfig: replace PPC_OF with PPC

The PPC_OF is a ppc specific option which is used to mean that the
firmware device tree access functions are available. Since all the
ppc platforms have a device tree, it is aways set to 'y' for ppc.
So it makes no sense to keep a such option in the current kernel.
Replace it with PPC.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/Kconfig

@@ -421,7 +421,7 @@ config MTD_NAND_ORION
 
 config MTD_NAND_FSL_ELBC
 	tristate "NAND support for Freescale eLBC controllers"
-	depends on PPC_OF
+	depends on PPC
 	select FSL_LBC
 	help
 	  Various Freescale chips, including the 8313, include a NAND Flash