dt-bindings: i2c: convert i2c-mpc to json-schema

Convert i2c-mpc to YAML.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>