i2c: core: Move ACPI gpio IRQ handling into i2c_acpi_get_irq

It makes sense to contain all the ACPI IRQ handling in a single helper
function.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>