ixgbe: Add a PHY power state method

This new method will control the PHY power state.  You pass in the
state you wish to change to (ether on or off).  For cases where this
method is not used the current PHY power state behavior is maintained.

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>