bcma: gpio: enable GPIO IRQ domain on BCM5301X

Just like on BCM47XX arch, BCM5301X also has ChipCommon with IRQ for
GPIOs. Now we have interrupts working on BCM5301X we can finally make
use of it. This has been successfully tested on 5 different devices
(Buffalo, Luxul, Netgear).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>