nouveau: add PRIME support

This adds prime->fd and fd->prime support to nouveau,
it passes the SG object to TTM, and then populates the
GART entries using it.

v2: add stubbed kmap + use new function to fill out pages array
for faulting + add reimport test.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_fence.c

@@ -573,7 +573,7 @@ nouveau_fence_init(struct drm_device *dev)
 	/* Create a shared VRAM heap for cross-channel sync. */
 	if (USE_SEMA(dev)) {
 		ret = nouveau_bo_new(dev, size, 0, TTM_PL_FLAG_VRAM,
-				     0, 0, &dev_priv->fence.bo);
+				     0, 0, NULL, &dev_priv->fence.bo);
 		if (ret)
 			return ret;