QoS: Modify data structures and function arguments for scalability.

QoS add requests uses a handle to the priority list that is used
internally to save the request, but this does not extend well. Also,
dev_pm_qos structure definition seems to use a list object directly.
The 'derivative' relationship seems to be broken.

Use pm_qos_request objects instead of passing around the protected
priority list object.

Change-Id: Ie4c9c22dd4ea13265fe01f080ba68cf77d9d484d
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>