bcma: add boardinfo struct

This struct contains information about the board, the chip is running
on. The struct is filled for PCIe devices and SoCs. This information is
used by b43 and will be used by brcmsmac soon.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Tested-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>