Port of_find_i2c_device_by_node() from Linux in order to allow looking
i2c_client up by corresponding DT node. Useful for interacting with
identical raw/driverless I2C devices that are not found on the same
bus between board variants.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>