ixgbe: add MAC and PHY support for x540

Adds the new x540.c file and Aquantia 1202 PHY for X540 support.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>