nouveau/acpi: hook up to the MXM method for mux switching.

this hooks up nouveau to the MXM mux switching method.

With this in place I can switch the LVDS MUX on my T410s,
I expect we need a bit more work for other laptops.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/Kconfig

@@ -11,6 +11,7 @@ config DRM_NOUVEAU
 	select FRAMEBUFFER_CONSOLE if !EXPERT
 	select FB_BACKLIGHT if DRM_NOUVEAU_BACKLIGHT
 	select ACPI_VIDEO if ACPI && X86 && BACKLIGHT_CLASS_DEVICE && VIDEO_OUTPUT_CONTROL && INPUT
+	select MXM_WMI if ACPI
 	help
 	  Choose this option for open-source nVidia support.