dt-bindings: arm: Convert Renesas board/soc bindings to json-schema

Convert Renesas SoC bindings to DT schema format using json-schema.

v2.1 [Simon Horman]
- rebased on renesas-devel-20181204-v4.20-rc5
  + Added r8a7744 development platform and SoM
  + Correct RZ/G2E part number
- Update MAINTAINERS

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>