mlxsw: Add PCI bus implementation

Add PCI bus implementation for Mellanox Technologies Switch ASICs. This
includes firmware initialization, async queues manipulation and command
interface implementation.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Elad Raz <eladr@mellanox.com>
Reviewed-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>