drm/amdgpu: add thick tile mode settings for Oland of gfx6

Adding thick tile mode for Oland to prevent UMD from getting mode value 0

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Tested-by: Hui.Deng <hui.deng@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>