bcma: add PCIe host controller

Some SoCs have a PCIe host controller to make it possible to attach
some other devices to it, like an other Wifi card.
This code was tested with an Netgear WNDR3400 (bcm4716 based), but
should work with all bcma based SoCs.

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