watchdog: tegra: move init to subsys_initcall

watchdog: tegra: move init to subsys_initcall

Move watchdog to subsys init to allow it to catch issues during
probing later devices.

Reviewed-on: http://git-master/r/433782
(cherry picked from commit fb1ee3a0aba6d06ea2732e804f3a41448731a4bb)

Change-Id: I972a4177445f0050ca50433b3fdaea80e0cf28c3
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Arun Kannan <akannan@nvidia.com>
Reviewed-on: http://git-master/r/454848
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Mitch Luban <mluban@nvidia.com>
Tested-by: Mitch Luban <mluban@nvidia.com>
GVS: Gerrit_Virtual_Submit