qed: remove unused qed_hw_info::port_mode and QED_PORT_MODE

Struct field qed_hw_info::port_mode isn't used anywhere in the code, so
can be safely removed to prevent possible dead code addition.
Also remove the enumeration QED_PORT_MODE orphaned after this deletion.

Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>