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>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index fef11f3..bb3ff43 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -67,6 +67,15 @@
 
 endchoice
 
+config DM
+	default y
+
+config DM_GPIO
+	default y
+
+config DM_SERIAL
+	default y
+
 config RAMBASE
 	hex
 	default 0x100000