drm/amdgpu/userq: prevent runtime pm when userqs are active

Similar to KFD, prevent runtime pm while user queues are active.

Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>