PM / QoS: cleanup FLAGS notifiers during removing

DEV_PM_QOS_FLAGS was introduced in commit
c92b96f94cdc26e33ea490a9a0e02c16988a6dd6, but it was forgot to remove
in dev_pm_qos_remove_notifier().

So without this patch, kernel will enter an endless loop in
notifier_chain_register() when reloading a module multiple times.

Bug 1421146

Change-Id: I6b98fe57a70f172d110cc5f257ce4f853a447802
Signed-off-by: Bryan Wu <pengw@nvidia.com>
Reviewed-on: http://git-master/r/347823
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
PM / QoS: check NULL and ENODEV on power.qos

fix kernel panic when qos is not null

Bug 1442069
Bug 1430231

Change-Id: I8810009e8f2a72730cfb253b245434d9e0806b9c
Signed-off-by: pchiang <pchiang@nvidia.com>
Reviewed-on: http://git-master/r/357069
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/360175
GVS: Gerrit_Virtual_Submit