Additional properties actually might appear (e.g. power-domains) so
describe all typical properties, reference generic i2c schema and use
unevaluatedProperties to fix dtbs_check warnings like:

  arch/arm64/boot/dts/freescale/imx8mn-evk.dt.yaml: i2c@30a20000:
    '#address-cells', '#size-cells', 'pmic@25' do not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>