PM: QoS: Drop the PM_QOS_SUM QoS type

The PM_QOS_SUM QoS type is not used, so drop it along with the
code referring to it in pm_qos_get_value() and the related local
variables in there.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Tested-by: Amit Kucheria <amit.kucheria@linaro.org>