drm/amdgpu/userq: handle runtime pm

Take a reference when we create a queue and drop it
when we destroy the queue.  We need to keep the device
active while user queues are active.

Reviewed-by: Prike Liang <Prike.Liang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>