dt-bindings: i2c: mxs: Pass ref and 'unevaluatedProperties: false'

Running 'make dtbs_check DT_SCHEMA_FILES=i2c-mxs.yaml' throws
several schema warnings such as:

imx28-m28evk.dtb: i2c@80058000: '#address-cells', '#size-cells', 'codec@a', 'eeprom@51', 'rtc@68' do not match any of the regexes: 'pinctrl-[0-9]+'
	from schema $id: http://devicetree.org/schemas/i2c/i2c-mxs.yaml#



Fix these warnings by passing a reference to i2c-controller.yaml#
and using 'unevaluatedProperties: false' just like the yaml bindings
of other I2C controllers.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>