i2c: core: Deprecate of_node in struct i2c_board_info

i2c: core: Deprecate of_node in struct i2c_board_info

Two members of the same or quite similar semantics is quite confusing
to begin with. Moreover, fwnode covers all possible firmware descriptions
that Linux kernel supports. Deprecate of_node in struct i2c_board_info,
so users will be warned and in the future there is a plan to convert
the users and remove it completely.

Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>