drm/amdkfd: Encapsulate DQM functions in ops structure

This patch does some re-org on the device_queue_manager structure. It takes out
all the function pointers from the structure and puts them in a new structure,
called device_queue_manager_ops. Then, it puts an instance of that structure
inside device_queue_manager.

This re-org is done to prepare the DQM module to support more than one AMD APU
(Kaveri).

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>