drm/amdgpu: Enable second VCN for certain Navy Flounder.

Certain Navy Flounder cards have 2 VCNs, enable it.

Signed-off-by: Peng Ju Zhou <PengJu.Zhou@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>