dm: x86: Move driver model CONFIGs to Kconfig

Remove driver model CONFIGs from the board config headers and use Kconfig
instead.

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

arch/x86/Kconfig

@@ -67,6 +67,15 @@ config TARGET_GALILEO
 
 endchoice
 
+config DM
+	default y
+
+config DM_GPIO
+	default y
+
+config DM_SERIAL
+	default y
+
 config RAMBASE
 	hex
 	default 0x100000

include/configs/x86-common.h

@@ -22,11 +22,6 @@
 #define CONFIG_DISPLAY_BOARDINFO_LATE
 #define CONFIG_DISPLAY_CPUINFO
 
-#define CONFIG_DM
-#define CONFIG_CMD_DM
-#define CONFIG_DM_GPIO
-#define CONFIG_DM_SERIAL
-
 #define CONFIG_LMB
 #define CONFIG_OF_LIBFDT