ARM: BCM5301X: Add IRQs to Broadcom's bus-axi in DTS file

IRQ support for Broadcom's bus-axi driver bcma was merged into John
Linville's wireless tree and will show up in 3.19. This patch makes use
of this feature in the DTS file for the the BCM5301X SoCs. I left the
PCIe controller out, because this still needs some discussion.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>