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_mem.c

@@ -416,7 +416,7 @@ nouveau_mem_vram_init(struct drm_device *dev)
 
 	if (dev_priv->card_type < NV_50) {
 		ret = nouveau_bo_new(dev, 256*1024, 0, TTM_PL_FLAG_VRAM,
-				     0, 0, &dev_priv->vga_ram);
+				     0, 0, NULL, &dev_priv->vga_ram);
 		if (ret == 0)
 			ret = nouveau_bo_pin(dev_priv->vga_ram,
 					     TTM_PL_FLAG_VRAM);