bcm47xx: add support for bcma bus

This patch add support for the bcma bus. Broadcom uses only Mips 74K
CPUs on the new SoC and on the old ons using ssb bus there are no Mips
74K CPUs.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>