ixgbe: add support for interrupts from X550 external PHY

ixgbe: add support for interrupts from X550 external PHY

Orabug: 21669416

This patch adds support for receiving interrupts from a external copper
PHY for the X550 part.  This includes enabling, detection as well as
re-enablement.

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>
(cherry picked from commit 597f22d6aa46105d69648a5c042d1fabe182c6f6)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>