dt-bindings: timer: Add Tegra186 & Tegra234 Timer

The Tegra186 timer provides ten 29-bit timer counters and one 32-bit
timestamp counter. The Tegra234 timer provides sixteen 29-bit timer
counters and one 32-bit timestamp counter. Each NV timer selects its
timing reference signal from the 1 MHz reference generated by USEC,
TSC or either clk_m or OSC. Each TMR can be programmed to generate
one-shot, periodic, or watchdog interrupts.

Signed-off-by: Kartik <kkartik@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>