drm/nouveau: move out of staging drivers

There's really no good reason for us to be in here anymore, we have to
maintain this ABI anyway to avoid angering people.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 2418429..8ea3bca 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -71,6 +71,8 @@
 
 source "drivers/gpu/drm/radeon/Kconfig"
 
+source "drivers/gpu/drm/nouveau/Kconfig"
+
 config DRM_I810
 	tristate "Intel I810"
 	# !PREEMPT because of missing ioctl locking