gpu: nvgpu: make wdt timeout per-platform

gpu: nvgpu: make wdt timeout per-platform

Channel watchdog timeout is set to a costant value of 5s
as of now

Make this timeout platform specific and set it to 5s for gm20b
and 7s for gk20a

Bug 200133289

Change-Id: I6e7f0fed93a8d5b197ae46807131311196c6636f
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/810956
(cherry picked from commit f015c3db9aecf7756375a0529dad8cdbca964377)
Reviewed-on: http://git-master/r/814252
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Change-Id: If5cce458e28574bf1eaf7134bc3f123f5a632d4e
Reviewed-on: http://git-master/r/815983
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>