eeprom: at24: add support to fetch eeprom device property "size"

Obtain the size of the EEPROM chip from DT if the "size" property is
specified for the device.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Divagar Mohandass <divagar.mohandass@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>