PM QoS: Add disable parameter

For testing purposes it is useful to be able to disable
PM Qos.

Bug 1020898
Bug 917572

Reviewed-on: http://git-master/r/124667

Signed-off-by: Antti P Miettinen <amiettinen@nvidia.com>
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

Rebase-Id: Re2088674f90436e0b9dd74310d5cda1f9e2868e4

Change-Id: I266f5b5730cfe4705197d8b09db7f9eda6766c7c