bcma: get IRQ numbers from dt

It is not possible to auto detect the irq numbers used by the cores on
an arm SoC. If bcma was registered with device tree it will search for
some device tree nodes with the irq number and add it to the core
configuration.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>