drm/amdgpu/vcn4: Fix IB parsing with multiple engine info packages

There can be multiple engine info packages in one IB and the first one
may be common engine, not decode/encode.
We need to parse the entire IB instead of stopping after finding first
engine info.

Signed-off-by: David Rosca <david.rosca@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>