drm/nouveau: select POWER_SUPPLY

Ben H. reported that building nouveau into the kernel and power supply
as a module was broken.

Just have nouveau select it, like radeon does.
Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/Kconfig

@@ -13,6 +13,7 @@ config DRM_NOUVEAU
 	select ACPI_VIDEO if ACPI && X86 && BACKLIGHT_CLASS_DEVICE && VIDEO_OUTPUT_CONTROL && INPUT
 	select ACPI_WMI if ACPI
 	select MXM_WMI if ACPI
+	select POWER_SUPPLY
 	help
 	  Choose this option for open-source nVidia support.