Define extra dword for jpeg ring. Jpeg ring will allocate extra dword to store
the patch commands for fixing the known issue.

v2: dropping extra_dw for rings other than jpeg.
Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>