i2c: core: Switch to fwnode APIs to get IRQ

Switch to fwnode APIs to get IRQ. In particular this enables
a support of the separate wakeup IRQ on non-OF platforms.
The rest is converted just for the sake of consistency and
fwnode reuse.

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>