dm: x86: Convert Intel ICH6 GPIO driver to use driver model

Convert over this driver, using device tree to pass in the required
information. The peripheral is still probed, just the number of GPIO banks
and their offsets is in the device tree (previously this was a table in
the driver).

Signed-off-by: Simon Glass <sjg@chromium.org>

include/configs/coreboot.h

@@ -27,6 +27,10 @@
 #define CONFIG_SYS_EARLY_PCI_INIT
 #define CONFIG_DISPLAY_BOARDINFO_LATE
 
+#define CONFIG_DM
+#define CONFIG_CMD_DM
+#define CONFIG_DM_GPIO
+
 #define CONFIG_LMB
 #define CONFIG_OF_LIBFDT