bcma: add the core unit number

bcma: add the core unit number

Some SoCs have two pcie or gmac cores and we need to know the number of
the specific core on the bus. This is the case for the BCM4706.

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