arm: tegra: hotplug: modify down_delay

Modified the hot-plug governor down_delay to be 500ms instead of 2s

Bug 958978

Change-Id: I55b5a4994f8e4564879cfd206fc683ff6f32d9ac
Signed-off-by: Wen Yi <wyi@nvidia.com>
(cherry picked from commit dd477396f2762f871255fb9d0800431d7534754d)
Reviewed-on: http://git-master/r/111640
Reviewed-by: Sai Gurrappadi <sgurrappadi@nvidia.com>
Tested-by: Sai Gurrappadi <sgurrappadi@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
Reviewed-by: Yu-Huan Hsu <yhsu@nvidia.com>