drm/radeon: force the UVD DPB into VRAM as well

Seems to be mandatory for WMV playback.

Bugs: https://bugs.freedesktop.org/show_bug.cgi?id=100510



Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>