arm: vt8500: gpio: Devicetree support for arch-vt8500

Converted the existing arch-vt8500 gpio to a platform_device.
Added support for WM8505 and WM8650 GPIO controllers.
Replaced existing readl/writel calls with _relaxed variants.
Replaced existing unsigned variables with u32 to match register size.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index ba7926f5..a00b828 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -183,6 +183,12 @@
 	  Say yes here to support the STA2x11/ConneXt GPIO device.
 	  The GPIO module has 128 GPIO pins with alternate functions.
 
+config GPIO_VT8500
+	bool "VIA/Wondermedia SoC GPIO Support"
+	depends on ARCH_VT8500
+	help
+	  Say yes here to support the VT8500/WM8505/WM8650 GPIO controller.
+
 config GPIO_XILINX
 	bool "Xilinx GPIO support"
 	depends on PPC_OF || MICROBLAZE