gpio: 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: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -383,7 +383,7 @@ config GPIO_XGENE_SB
 
 config GPIO_XILINX
 	tristate "Xilinx GPIO support"
-	depends on OF_GPIO && (PPC_OF || MICROBLAZE || ARCH_ZYNQ || X86)
+	depends on OF_GPIO && (PPC || MICROBLAZE || ARCH_ZYNQ || X86)
 	help
 	  Say yes here to support the Xilinx FPGA GPIO device