drm/amdgpu: remove asymmetrical irq disabling in vcn 4.0.5 suspend

There is no irq enabled in vcn 4.0.5 resume, causing wrong amdgpu_irq_src status.
Beside, current set function callbacks are empty with no real effect.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Saleemkhan Jamadar <saleemkhan.jamadar@amd.com>
Reviewed-by: Veerabadhran Gopalakrishnan <Veerabadhran.Gopalakrishnan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>