DeviceTree updates for v4.18:

- Sync dtc with upstream version v1.4.6-21-g84e414b0b5bc. This adds new
  warnings which are either fixed or disabled by default (enabled with
  W=1).

- Validate an untrusted offset in DT overlay function
  update_usages_of_a_phandle_reference

- Fix a use after free error of_platform_device_destroy

- Fix an off by 1 string errors in unittest

- Avoid creating a struct device for OPP nodes

- Update DT specific submitting-patches.txt with patch content and
  subject requirements.

- Move some bindings to their proper subsystem locations

- Add vendor prefixes for Kaohsiung, SiFive, Avnet, Wi2Wi, Logic PD, and
  ArcherMind

- Add documentation for "no-gpio-delays" property in FSI bus GPIO master

- Add compatible for r8a77990 SoC ravb ethernet block

- More wack-a-mole removal of 'status' property in examples
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