dsa: Replace mii_bus with a generic host device

This change makes it so that instead of passing and storing a mii_bus we
instead pass and store a host_dev.  From there we can test to determine the
exact type of device, and can verify it is the correct device for our switch.

So for example it would be possible to pass a device pointer from a pci_dev
and instead of checking for a PHY ID we could check for a vendor and/or device
ID.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>