x86: Convert INTEL_ICH6_GPIO to Kconfig

This converts Intel ICH6 GPIO driver to Kconfig, and add it to the
imply list of platform drivers.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 15135e5..63951e0 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -67,6 +67,12 @@
 	  driver from the common Intel ICH6 driver. It supports a total of
 	  95 GPIOs which can be configured from the device tree.
 
+config INTEL_ICH6_GPIO
+	bool "Intel ICH6 compatible legacy GPIO driver"
+	depends on DM_GPIO
+	help
+	  Say yes here to select Intel ICH6 compatible legacy GPIO driver.
+
 config IMX_RGPIO2P
 	bool "i.MX7ULP RGPIO2P driver"
 	depends on DM