drm/nv50: initial work to allow multiple evo channels

This doesn't work yet for unknown reasons.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -689,6 +689,7 @@ struct drm_nouveau_private {
 	struct backlight_device *backlight;
 
 	struct nouveau_channel *evo;
+	u32 evo_alloc;
 	struct {
 		struct dcb_entry *dcb;
 		u16 script;

drivers/gpu/drm/nouveau/nouveau_ramht.c

@@ -114,7 +114,7 @@ nouveau_ramht_insert(struct nouveau_channel *chan, u32 handle,
 		      (gpuobj->engine << NV40_RAMHT_CONTEXT_ENGINE_SHIFT);
 	} else {
 		if (gpuobj->engine == NVOBJ_ENGINE_DISPLAY) {
-			ctx = (gpuobj->cinst << 10) | 2;
+			ctx = (gpuobj->cinst << 10) | chan->id;
 		} else {
 			ctx = (gpuobj->cinst >> 4) |
 			      ((gpuobj->engine <<