net: ethernet: bgmac: Add platform device support

The bcma portion of the driver has been split off into a bcma specific
driver.  This has been mirrored for the platform driver.  The last
references to the bcma core struct have been changed into a generic
function call.  These function calls are wrappers to either the original
bcma code or new platform functions that access the same areas via MMIO.
This necessitated adding function pointers for both platform and bcma to
hide which backend is being used from the generic bgmac code.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>