MIPS: BCM47xx: Read board info for all bcma buses

Extra bcma buses may be totally different models, see following dump:
boardtype=0x0646
pci/1/1/boardtype=0x0545
pci/2/1/boardtype=0x62b
We need to detect them properly to allow drivers apply some board
specific hacks.

[ralf@linux-mips.org: folded in Rafal's fix.]

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/10028/
Patchwork: https://patchwork.linux-mips.org/patch/10048/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>