bnxt_en: Handle ethernet link being disabled by firmware.

On some 200G dual port NICs, if one port is configured to 200G,
firmware will disable the ethernet link on the other port.  Firmware
will send notification to the driver for the disabled port when this
happens.  Define a new field in the link_info structure to keep track
of this state.  The new phy_state field replaces the unused loop_back
field.

Log a message when the phy_state changes state.  In the disabled state,
disallow any PHY configurations on the disabled port as the firmware
will fail all calls to configure the PHY in this state.

Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>