drm/amdkfd: Clean up the data structure in kfd_process

A list of per-process queues is maintained in the
kfd_process_queue_manager, so the queues array in kfd_process is
redundant and in fact unused.

Signed-off-by: Yong Zhao <yong.zhao@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>