CTA preemption needs to be enabled by setting a value in context. Set
it for gm20b.
Bug 200063473
Bug 1517461
Change-Id: I080cd71b348d08f834fd23ebbe7443dba79224db
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/661299