vulkan/video: hevc: b-frames can be reference or not
b-frames can be considered as reference, so the NAL type should refer to reference type and either RASL or TRAIL depending on the irap_pic_flag. Fixes: 72f52329 ("vulkan/video: add a nal_unit lookup for hevc") Reviewed-by:Hyunjun Ko <zzoon@igalia.com> Part-of: <mesa/mesa!28657> (cherry picked from commit 363a90d0)