radeonsi/vcn: try to use dpb_type tier2 for av1 encoding in vcn5
What does this MR do and why?
dpb_type tier2 is using app dpb management scheme, av1 encoding
can work on vcn5 now for single reference case and disabled now
for preparing next step development.
Signed-off-by: Ruijing Dong <ruijing.dong@amd.com>