bcma: mips: show also disabled IRQs

Some cores do not have a IRQ assigned and some do not support when an
IRQ is assigned to them, this is now handled and printed out in the
code.

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