gpu: nvgpu: cancel all wdt timeouts while handling SCHED errors

gpu: nvgpu: cancel all wdt timeouts while handling SCHED errors

A SCHED error might cause multiple channels' watchdogs to trigger
simultaneously

Hence, to avoid this conflict cancel watchdog timeout on all
channels before recovering from SCHED errors

Also, define API gk20a_channel_timeout_stop_all_channels()
to cancel wdt timeout on all channels

Bug 200133289

Change-Id: I8324c397891f0a711327b77d0677cd6718af6d01
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/810959
(cherry picked from commit 1501d972d4ab1546737472d0469faacb6ed9eb18)
Reviewed-on: http://git-master/r/814255
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Reviewed-on: http://git-master/r/825506
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>