dt-bindings: misc: Add Tegra186 MISC registers bindings

NVIDIA Tegra186 MISC register block

The MISC register block found on Tegra186 SoCs contains registers that can be

used to identify a given chip and various strapping options.

Required properties:

- compatible: Must be:

  - Tegra186: "nvidia,tegra186-misc"

- reg: Should contain 2 entries: The first entry gives the physical address

       and length of the register region which contains revision and debug

       features. The second entry specifies the physical address and length

       of the register region indicating the strapping options.