i2c: Add nop fwnode operations

Add nop variants of i2c_find_device_by_fwnode(),
i2c_find_adapter_by_fwnode() and i2c_get_adapter_by_fwnode() for use
without CONFIG_I2C.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>