watchdog: tegra: Add device tree support.

watchdog: tegra: Add device tree support.

Add compatible string.
Compute timer reg from timer regs base addr instead of device id.

Reviewed-on: http://git-master/r/433781
(cherry picked from commit ae30129714b1f9327e5f4b085413800bfbcbb194)

Change-Id: Ida3e00eff28244a1857fe43c479d7baed667c524
Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Arun Kannan <akannan@nvidia.com>
Reviewed-on: http://git-master/r/454847
Reviewed-by: Mitch Luban <mluban@nvidia.com>
Tested-by: Mitch Luban <mluban@nvidia.com>
GVS: Gerrit_Virtual_Submit