MIPS: BCM47xx: Register SSB fallback sprom callback

MIPS: BCM47xx: Register SSB fallback sprom callback

We are generating the prefix based on the PCI bus address the device is
on. This is done like Broadcom does it in their code expect that the the
bus number is increased by one. In the SB bus implementation used by
Broadcom the SB bus emulates a PCI bus so the kernel sees one PCI bus
more then in our implementation. We do not handle prefixes like sb/1/
yet as they are only used on the new bus which is not implemented yet.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2364/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>