ARM: tegra: define DT bindings for and instantiate timer

The Tegra timer provides a number of 29-bit timer channels, a single
32-bit free running counter, and in the Tegra30 variant, 5 watchdog modules.
The first two channels may also trigger a legacy watchdog reset.

Define a DT binding for this HW module, and add the module into the Tegra
device tree files.

Signed-off-by: Stephen Warren <swarren@nvidia.com>