bcma: make it possible to specify a IRQ num in bcma_core_irq()

This moves bcma_core_irq() to main.c and add a extra parameter with a
number so that we can return different irq number for devices with more
than one.

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