drm/amdkfd: Call kfd2kgd.set_compute_idle

User mode queue submissions don't go through KFD. Therefore we don't
know exactly when compute is idle or not idle. We use the existence
of user mode queues on a device as an approximation.

register_process is called when the first queue of a process is
created. Conversely unregister_process is called when the last queue
is destroyed. The first process that is registered takes compute
out of idle. The last process that is unregisters sets compute back
to idle.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Eric Huang <JinHuiEric.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>