ixgbe: Add X553 PHY FC autoneg support

This patch adds X553 flow control auto negotiation for fiber and
backplain.  To enable this new function pointers were added as well
as creating a function to dynamically set function pointer we can't
define only on MAC type.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>