bcma: mips: explicit assign IRQ numbers

The assignment of the IRQs to the cores of the chips by iterating over
the cores is complicated and causes problems with SoC like the BCM4706
with two GMAC core where just one should get a dedicated IRQ number.
Now the code assigns the same IRQs to the cores as the code from the
Broadcom SDK does. If the SoC is not know the current assigned IRQs are
only read out and an error message is printed.

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