net: aquantia: Cleanup pci functions module

Driver contained a dead code of maintaining multiple pci port instances.
That will never be used since for each pci function a separate NIC
instance is created.
Simplify this, making pci module only responsible for pci resource
management.
NIC initialization is also simplified accordingly.

Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>