drm/nouveau: fix ch7006 build

The ch7006 driver could be built even when nouveau was not enabled,
but the build fails in that case, so make it depend on DRM_NOUVEUA.

Also make the I2c encoder/helper chips menu depend on I2C (no build
error, just visual inspection).

ERROR: "drm_helper_probe_single_connector_modes" [drivers/gpu/drm/i2c/ch7006.ko] undefined!
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/Kconfig

@@ -30,11 +30,12 @@ config DRM_NOUVEAU_DEBUG
 	  via debugfs.
 
 menu "I2C encoder or helper chips"
-     depends on DRM
+     depends on DRM && I2C
 
 config DRM_I2C_CH7006
 	tristate "Chrontel ch7006 TV encoder"
-	default m if DRM_NOUVEAU
+	depends on DRM_NOUVEAU
+	default m
 	help
 	  Support for Chrontel ch7006 and similar TV encoders, found
 	  on some nVidia video cards.